If they like someone, that's a good reason.
If the character already has a role in the story which is NOT one of a "companion", then there's no "good reason" to ask to make it one, if not the usual misunderstanding that this is supposed to be some sort of dating sim.
I disagree. And it isn't just "hot" characters (replying also to your previous "fuckable" comment) cause there are unattractive ones that have been requested as well. For example Lump the Enlightened seems like he could be an interesting companion/mercenary due to his situation. And I have been an advocate for a Gobbo companion to be added. Furthermore, almost all requested characters have been ones that make some sense to join the party.
Abdirak doesn't have any particular loyalty to the Absolute and seems to bond with the main character, with some convincing or gold we could possible convince him that his god's will could align with us. Minthara has a whole wellspring of reasons she could be a companion with us. US was already a companion and is a cute brain doggo. And Volo or Alfira are Bards with existing interactions and a possibility to have even more complete arcs if they join the adventuring party. Overall it isn't based on fuckability (Even as some may simp over Halsin or Minthara) but their actual potential as a companion. Cause arguably there are many attractive NPCs in the game, but not many are asking for those characters to join us based on looks alone.
