Cause the book is basically psychological, and if Tom had the brainpower to realize that when you're up against an enemy whose power derives from self-loathing, loathing yourself all the time might not be such a good idea, then there goes the conflict and depth, and it devolves to smacking cavewights around. With the revelation in the latest book that (spoiler) nothing done out of love can ever aid the Despiser, even indirectly, he literally couldn't go wrong by turning his frown upside-down.

And that's not even getting to the stuff with the Earthblood. Seriously, Elena, you've gained complete omnipotence for the space of one wish, and the best you can think of is "resurrect the vengeful ghost of the morally conflicted apocalyptic ex-ruler because maybe he's mellowed out"? How about "I wish for a Friendly AI under the control of Revelstone"?