Many genres can be called trash for different reasons, lol. I hate rhytm\reaction games, from dancing and playing instruments to fromsoft titles. It's just I'm not build to enjoy them. But I love Diablo and would try to explain why.

Besides art direction of old Bliz and Matt Uleman's OST, I like these series for... them being a task in optimization. Some games like building and management simulators are straightforward about it, but there it only shows in the endgame of diabloids. You are to think of theoretical ways of bettering your build, but also inventing the best way to farm X things in the least time possible to make it. I haven't topped the ladder too many times for looking up others' builds and copying them steals half of enjoyment from experimenting with it. It touches the same buttons in me as rewriting code for better performance does, and the only downside is me, a meatbag, executing it line by line, that you called mindless for a reason. I just reiterate through my idea before I see the predicted outcome.

That sort of enjoyment also surfaces in other games, like old shooters and RPGs, where I find ways to abuse the system and benefit from it. It's a casual version of what speedrunners are into. Finding the best\fastest way to do X, but only for you to test and observe.