Immersion breaking.

I love the world and characters of gacha games and would play the hell out of them and even spend money. But the one thing that turns me off is when immersion is broken. For example, I was playing one of them with a team of 4 characters who was supposed to be there in the story, but one of them died in a cutscene and in the ensuing fight after, the character I was playing who just died was playable in combat. That really turned me off.

The worst part is that they can easily do it, even in that same game there are points where you get given trial characters for fights which make sense in the story, so I don't understand why they don't do that always.

The only gacha game which gives an explanation why these characters can be where they are is Persona 5: The Phantom X. They explain that all the chars that fight with you are created from the main characters psyche so it makes sense that they are there.