Time. No studio has unlimited time and resources. Decisions have to be made to exclude some things in order to produce a product that appeals to a large audience at a reasonable time.
So yes some 0.1% of the population will be disappointed their pet customization is not included but hopefully the entirety of the game is good enough they will buy the game regardless. This isn’t an all or nothing choice.
It doesn't work like that with RPG genre, because the point is having choice, the less choice you have the worse the game objectively is, like I already said before, having a choice that you won't take makes the choice that you will take worth more.
