I would say (and this is just my opinion), that the over-obsession with IP has to do largely with the fact that our culture and society, more so now than ever, feels the need to be told how to think and feel. Things of originality scare people today because it requires them to fill in the gaps with their own experiences or conceptions of how things are. I think this is largely why most studios are pumping our reboots, sequels, prequels, etc. They're safe. Rather than gamble on a new, untested idea, they know that people will just eat up the next installment of "_______" franchise because they went ga-ga for the last one. And that belief is showing itself in the parks. Rather than trusting that guests will have a great time at this attraction featuring unfamiliar characters, they just take whatever made "good" money at the B.O. and think to themselves, "hey, they loved the movie, they'll love the ride even more!" But that's the problem. It's an unsustainable trend. Eventually they'll run out of space to put all the new movie-based attractions and possibly run the risk of getting desperate and axe something long-standing and beloved just to make the immediate audience happy.
I wouldn't necessarily go that far; I don't think the public itself is explicitly to blame, particularly in an era where some may argue we're more self-expressive than we've been in a long time thanks to the boom in communications technology (there are lots of debates to be had about how expressive we are if we use the same platforms, but it's still the era of readily available information, after all). I think Occam's Razor should always apply: the head honchos at corporate pinch some pennies by being slow on updating or upkeeping certain attractions, they see big box office returns from the film division, they see some attractions at the parks getting older and more worn from corporate's neglect, they've now created a feedback loop that lets them put two-and-two together to equal new revenue.
As the dollar amounts spent on things like tentpole movies keep going up, the perceived need to advertise more, to sell more merchandise, to use the rides as advertising, to not take major risks keeps getting stronger and stronger; it's not that the public would never accept a new idea, it's that the studios are going in so deep from a financial perspective that they're scared to take those risks, and it's a fair fear to have in an era where business and finance is driven by a mindset of "what do the next two quarterly projections look like?" A bad two quarters could've outsed Iger at any random point, for example, so he was sure to buy up properties of familiar stories and characters and market the high holy hell out of them. The public may desire something newer than more Star Wars/Marvel/etc., but as long as studios keep trying to outdo one another with huge budget spectacles, they're not likely to take a chance on a new Star Wars.
@britain , you're certainly right about the size of the WS, but that's just it: in a themed environment, we shouldn't have to worry about potential eyesores or out of place marketplaces. I'm not saying any new ride would automatically be awful, but the entire point of theming and planning your environment is to iron out inconsistencies and to maintain what the folks at WED always called the "architecture of reassurance". It's not to say that such attractions would automatically be failures, but it's just extrapolating concern based on Disney's recent track record. Frozen alone doesn't suddenly shatter World Showcase and its ambiance, but I fear it as part of a trend.
@CaptainAmerica, I think you just inadvertently made the argument for newer rides instead of IPs for a lot of people. Yes, before they were released as movies not a ton of people knew the story of The Snow Queen nor did a ton of people read enough comics to know about the Guardians of the Galaxy. While they weren't financial investments on the level of Star Wars Episode VII or the Avengers movies, they were still slight gambles, Disney hoping that people would see that Disney animation was making Frozen and that Marvel Studios was making GotG, take that as a positive sign, and say "ok, I may not know these stories/characters, but I trust those studios so I'll give them a try". They paid off. Why should that mentality not apply to the theme parks, then? The Disney theme park brand name still has plenty of cultural cache, and Disney has a history of taking original concepts and turning them into highly successful theme parks, rides, and attractions, so why not take some calculated risks and gambles there rather than falling back on what's considered "safe", albeit potentially transient?