I suppose first because it is filled with false doctrine and sentimental rubbish. It is unanchored in anything other than pure sentiment, contradicts the scriptures, and attributes motives to Heavenly Parents which are held by the author. It is worse than useless, it is misleading.
The numerosity argument takes groups who could not possibly be the audience for his book and makes them the statistical weight from which he reaches his conclusion. He takes folks who lived during the Nephite centuries of peace, the City of Enoch, and those who will live during the Millennium (whose numbers he speculates to be in the billions), then adds to those numbers all who die before the age of 8 (also a speculative but big number), then, after claiming the speculative total of all these will be far, far greater than those who merely slog along in mortality like us, he concludes that the odds are you're going to be exalted. Here's the logical fallacy of that whopper: First, the Nephites in ancient history didn't read the book. They're NOT in his audience. Neither was the City of Enoch's hosts; nor are the Millennial folk; nor are any of those who die before age 8. Meaning that the argument, IF it had validity, is an argument that THEY are going to be exalted. Not YOU. That is, the speculative total of those hosts are the ones who will benefit from their lives' condition. But none of them are readers of the book. So if the argument fits, then the title should have been: "Odds Are They're Going To Be Exalted."
Second, the argument for the numbers is wholly speculative. We don't have a census for any of the prior Nephite, Enoch, City of Melchizedek, etc. populations. So without an actual number, we can't even make the argument. His conjecture for the Millennium is based upon Elder Bruce R. McConkie's speculation about the numerosity of that group. Repeating what Elder McConkie admits is his conjecture does not reduce it to fact. We simply can't say what the final numbers will be for these other groups.
Third, he conflates the promise of "salvation" with "exaltation." So far as I know there are no children under age 8 who have been sealed in marriage - a condition required for exaltation. Without an eternal marriage they are separate, single and angels; NOT exalted. (D&C 132: 16-17.) It is a quantum leap unsupported by scripture to conflate the promise of salvation for those who die before age 8, or who were not sealed in marriage from any of the other populations about which he speculates, with the promise of exaltation.
Fourth, he gives one bit of caution in his Introduction which the average reader will not catch. That caution is: "What follows is my perception of God's nature...." p. xiv. That caution should be in BOLD and capitalized. In other words, the whole book is based upon his sentiments about God. These unanchored sentiments are NOT and never will be doctrine. They are just some guy's effeminate effort to avoid the rigors of confronting the narrowness, straitness and fewness of the Gospel's takers.
Going then to his sentiments about God, he writes: "The thought that God would promote something that would ensure that the vast majority of His children would never again be able to dwell in His presence is incomprehensible. And the assumption that our mother in heaven would idly sit back and allow such a guaranteed flop to eternally strip her of any interaction with her spirit offspring is equally unfathomable. Such could not --- and did not-- happen!"
There's not a stitch of support for this awesome conclusion. How does he know that? How does he presume to speak about a "mother in heaven" about whom nothing has been revealed? How does he know that she is not the champion of the plan? How does he know that she isn't absolutely persuaded that obedience to the laws of perfection are the only protection of her children who do obey? How does he not recognize that to dwell with someone living a higher law, when the person refuses to obey that higher law, is more miserable than being cast out? (Morm. 9: 4.) How does he fail to recognize that throughout nature from the hosts of animals born, relatively few ever reach adulthood and reproduce? Again, this natural process is a symbol of God's own great plan, is it not? (Moses 6: 63.) If so, why, if God cares with sentimentality about all His creations (i.e., that they fill the measure of their creation and have joy in their posterity), then why not let all them reproduce as adults? After all it takes about 10,000 sea turtles before you get a successful reproducing adult. Pretty much the case with frogs, sea life generally, and wildebeests - well, their young are essentially the roving McDonald's menu for all the African meat-eaters.
When he doesn't like a parable told by CHRIST, he attributes it to Matthew and dismisses it as Matthew's conjecture about numbers. (See footnote 2 on the top of page 133 of Odds Are You're Going To Be Exalted)
He absolutely contradicts Christ when he claims, without any support other than his own sentiment, "God does not require perfection of us in order for us to gain exaltation." (page 13.) But Christ commanded: "Therefore I would that ye should be perfect even as I, or your Father who is in heaven is perfect." (3 Ne. 12: 48.)
He is a PhD in Theology. That education has done violence to his ability to see what the scriptures teach. Instead of using that education properly (i.e. to understand the fallacies of man's reasoning as they apply their philosophy), he has instead become persuaded by it and decided to measure truth by this damaging set of errors.
He thinks that if "most" people are lost then the plan is a failure. The measure of the Gospel's success does not lie in numerosity. It lies in the fact that if the whole of creation produces but one successful couple, then it will have all been worth it. Even then, if only one couple were exalted, then you still have an infinite number to follow, because they are by definition infinite and eternal as long as they produce seed.
I have marked up my copy for the first couple of chapters, then just relented and read it without a running commentary in the margins. But the book was an insult to my understanding of the truth. It attempts to urge the Calvinist notion of "irresistible grace" in new clothes. It attempts to give life to "grace" as Martin Luther championed the concept in LDS garb. It is a litany of Evangelical/Protestant philosophy mingled with scripture. And most astonishing of all, this cacophony of error is published by the good people at Deseret Book, as if its creeds were not included among those denounced by the Savior in His first visit with Joseph in the Grove.
I keep running in my mind: "Perhaps you do not believe in this great being Alonzo Gaskill proposes, who is surrounded by myriads of beings who have been saved, not for any act of theirs, but by His good pleasure?"
And the response thunders back: "I do not! I cannot comprehend such a being!"
I cannot recall where that dialogue, which is now simply part of my consciousness, came from. But it seems somehow sacred to me, coming from some source I trusted. Something which goes back long before 1990. But, alas, when I try to pin it down it eludes me.
I could go on, but I think it would degenerate into incautious words which will offend the average reader. Given my upbringing in Idaho, I will soon be making scatological references to bovine feces, reverting back to the lexicon of my pre-conversion youth. So I will meekly stop and settle back into the day's work.
I hope that answers the question.