Because hardly anybody writes about Alibaba's little descent into Depravity.
Aladdin doesn't know.
He can talk all he wants about Falling and Depravity, but he doesn't know. Alibaba does. Not well, but he does. Safely tucked in the back of his memories is the one where he Fell, where he had his little taste of Depravity, and here and there that memory resurfaces and reminds him what it felt like.
There had been a voice - a voice of a woman - whispering comforting things into his ear. There had been warmth. All the grief, all the despair had been so taxing on his body, and Depravity offered rest. It offered peace. Depravity was so easy, so much so that it was nearly physically impossible not to Fall. But Aladdin doesn't know any of this - and he can't, not ever, not until he experiences Falling firsthand.
And so because Alibaba knows what Depravity was like, even a little bit, he finds himself pitying everyone everywhere who couldn't help but Fall. Hakuryuu, Dunya, Judal. All of them. They're addicted to it. They've been Depraved for so long that there's no way out, that they physically can't live without it in their system.
And now Alibaba lies here - wherever here is, exactly, it's too damn dark to tell - and he forgives Hakuryuu for 'killing' him, strange as it may sound. Because he remembers what it was like when Depravity told him to fight Aladdin. He feels sorry for the poor prince of Kou, and hopes that Aladdin does as well. After all, Solomon's Wisdom is his only chance at salvation.
And yes, Alibaba is forever grateful for saving him from Depravity, and so much more - he only wishes that Aladdin would stop going around and talking like he knows about Depravity. He doesn't - and Alibaba hopes with all his heart that he never gets the chance to.