Piecing together the reports from THR, Deadline, and other news outlets this is the timeline of what likely happened:
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Disney’s and Sony’s original deal had concluded after “Far From Home” where Disney was compensated 5% of every first dollar and Kevin Feige oversaw both of Sony’s Spider-man films but did not get any producer fee from Sony.
When it was time to renegotiate a new deal, Sony asked Feige to bring their Sony properties, specifically Venom, into the MCU and him to oversee their future Spider-centric projects. Fiege who had been noticeably hesitant in interviews last year to include Venom in the MCU, began opening up to the idea. But having more movies added to his already full plate, Feige understandably is not going to want to spend a lot of his time working for Sony, not only in their next Spider-man films but now also for Venom and all their other upcoming films for the same “pro bono” rate he did for the last two Spidey films.
Disney steps in and tells Sony if they want Feige, a Disney employee, to go to another studio and oversee all their upcoming Spider films including integrating them all into the MCU, they would like to see a 50/50 split on financing and revenue.
Sony who had been paying Disney only 5% balked at that request, possibly hoping Feige could do the extra work for the same rate from the previous deal they had in place.
Negotiations between the two inevitably went as far down as Disney not wanting to go any lower than 30% and Sony still refusing. Deal breaks down.
Sony then issued a statement that Spider-man can no longer be part of the MCU because Feige is too busy working on Disney’s new IPs.