Because they rarely do things like this *just* to be PC. I think the change likely has an element of modernizing the ride and attitudes toward women, but still, profit-driven with movie tie-ins and room for expansion of future movies. It costs a lot to shut down and redo ride scenes. Unless it's reaaaally blatantly offensive, I doubt they would go through all of this if that were the sole reason.
You don't know with certainty that future guests will like the ride without movie tie-ins. Actually, they may like the ride--but maybe they don't understand why it's different from the movie. Maybe people were commenting how great it'd be with more movie tie-in. Again--Disney will do what it wants, and if an immersive theme park experience with more movie tie-ins is their direction, then so be it. How do little kids feel about Country Bear Jamboree today? I liked that movie as a kid. Is it still a hot film and hot attraction?
Enough to rival HoP backlash? Enough to overwhelm Disney to change this ride for one reason and one reason only?
Eh, whatever. They will always need to depend on a blend of both (not going to argue on the percentage of each, but they need both). Plenty of things in the parks still that aren't strictly movie-based. Although my guess is that future movie overlays will continue to do well because people LOVE IP--give them what they want, and if they keep going, Disney will keep giving. *If* the parks before this truly were not predominantly IP-based, it's a fine experiment at least for now to see if more movie tie-ins across the park will increase profit.
As far as business, merchandise is a huge part of what it's all about. Who cares if you pay $100 or whatever to enter MK and ride rides? Not the execs and shareholders. They make money off of guests buying food and merch during their time in park. Of course merchandise is huge--can't blame a business for wanting to capitalize on a tactic that continues to work.