People like porn involving characters they like. Look at all the rule 34 content. Games give you a chance to engage with the characters before the fucking.

There is also a bit of T&D as you build anticipation while playing the game.

I’d imagine it’s sort of like reading porn rather than watching porn. Different people are activated by different things.

More role play I suppose?

Immersion and customizability

I imagine to some its sort of like gambling? Hard to say.