Sony didn't want to share a cut of its biggest property, obviously, and Disney wanted more of what is now (and what has always been) the most popular character in the Marvel universe. Spider-Man: Far From Home just spent a whole movie cementing Peter Parker at the center of the new MCU wheel, and Spider-Man is, along with maybe Thor, the biggest guaranteed hit Marvel has now that it's finished decimating its core team by the end of Avengers: Endgame.
It's kind of nuts of Sony to push Disney away at this point, since Kevin Feige has produced nothing but home runs for the MCU this entire time, but clearly, Sony thinks it has a handle on things after Far From Home cleared Skyfall to become the studio's highest-grossing movie ever. Plus, they just got an animated film Oscar trophy with last year's game-changing Spider-Man: Into the Spider-Verse.
One upside to all this is that future Spider-Mans probably won't have the specter of Tony Stark looming over them, something that has hampered the character since Civil War. And really, the surprise ending of Spider-Man: Far From Home sets up a future for the character that's entirely Spider-Man-centric, despite the movie also trying to turn him into the next Iron Man. Sony has two more Spider-Man movies in the works, starring Tom Holland and set to be directed by Jon Watts, and a slew of other Spider-properties, including the Venom sequel, Jared Leto's Morbius, a Kraven The Hunter movie, and whatever's going on with that Silver Sable and Black Cat joint. But it's risky for the studio, especially at this point, to part with Disney, which owns a frighteningly large stake in the entertainment business at-large.
Sony released an especially spicy statement on Twitter late Tuesday night after everyone had enough time to completely freak out, essentially saying what a shame it is that, with Disney's new studio acquisitions and Disney+ plans, Feige probably has way too much on his plate right now to pay attention to a little spider: "We are disappointed, but respect Disney’s decision not to have him continue as a lead producer of our next live action Spider-Man film. We hope this might change in the future, but understand that the many new responsibilities that Disney has given him -- including all their newly added Marvel properties -- do not allow time for him to work on [intellectual property] they do not own."