I will say, I do think both of these companies realistically shouldn’t have to lean so much on others IP though when they have a treasure trove of underutilized IP at their disposal. It never made sense that Universal is going with 3 Harry Potter lands instead of doing anything else with Jaws, Ghostbusters, Back to the Future.
A few things.
First, while Sony has been a great partner for Uni, Ghostbusters is not Universal owned. Like I said earlier, this goes back to opening day era and current really for all major theme parks.
Universal in the 90s did have various venues including major attractions based on those properties. While they can come back in other forms, and I would love to have some back, they do in fact represent them now in various ways. They are not exactly shunned or forgotten. Last year for example with live entertainment and night time spectacular, even an escape room in resort for BTTF. At a certain point, it is possibly diminishing returns.
That is it for those you mentioned but Uni also the deep cuts while Disney has chased recent only. Since Iger has been in charge you will rarely find anything at WDW referencing their legacy pre Mermaid 1989. Rarely, not absolute.
At Uni. Deep cuts still. i.e.Blues Brothers, Beetlejuice, Horror Make Up's content, American Graffiti, Marylin Manroe's film-based persona, Jay Ward Toons etc...)
Also at special events like HHN or the new Fan Fest nights you are seeing that property.
All of thse properties have live ent and photo ops and references each of the parks.
As far as Potter in three parks...Each has been a hit and the food and beverage alone more than worth the while. The attractions have even at their weakest done well. It nkt mutually exclusive. The success of Potter helped pitch the return of the legacy properties. Maybe more soon we can hope.
You see Potter in three theme parks for the same reason you have Star wars in multiple areas at Disney properties, Frozen and Mermaid represented in multiple parks woth rides and shows telling the same stories and songs as well as Lion King in the 90s in every Disney Theme Park somewhere.
Money and spreading the ways to captilize on it.