What does it matter in this game? In bg1-2 your choice of deity directly affected your powers and abilities, but here it seems like it's all about the domain (which make the hilarious option to create a healer who worships Bhaal). Am I missing something?
Actually, in BG1 their was no deity choice. BG2 added three kits for clerics of specific deities, but if you chose a generic cleric instead of one of those three deity selection had no effect. BG enhanced edition added the BG2 cleric kits into BG1. Some cleric spells where effected by alignment, but this was more of an Icewind Dale thing.
very informative but how does it answer my question?
It's a change in the D&D rules, moving from 2nd edition to 5e. In 5e alignment is in the process of being phased out, and has no mechanical effect (apart from a couple of magic items in the DMG that require specific alignments for attunement).
5e also does not have rigid rules about deities and domains. It has a list suggesting which domains suit which deities, but it is not a hard rule that players are required to follow.