Disney has a uneven way in theming rides. For every 7DMT they have a Goofy's Barnstormer, Primeval Whirl or Rock 'n' Roller Coaster. All off the shell, small coasters that are sparsely themed or put in a simple box.
Universal, most of the time, puts the ride up front. They'll theme it but won't hide it. It's fairly consistent and they are very successful in doing it that way. I think there is an excitement and joy in seeing the slides, I know what I'm into when choosing that ride/slide. But I don't want them to sit on a concrete parking lot but in a well themed environment. I think Universal strikes that balance quite well.
Another reason they couldn't build one mountain to slam on the slides on is that they decided to create a kind of spoke and wheel design for their water park, with the volcano as Cinderella's castle in the middle and the rides in themed lands around them paired with food and drink options. As far as I know this is unique, at least for the Orlando market.