Sony does. The only thing Marvel Studios did was offer up Kevin Feige to serve as a guiding hand to make a good movie but also make sure the direction fits with the MCU. But Sony finances, distributes, and has final creative control over the solo movies.
Sony also makes the majority of the profits. The only thing Marvel and Disney get is 5% of first-dollar gross which means they make 5% of whatever amount the movie makes on day one of its theater release. To put numbers into perspective... Far From Home made a total worldwide $1.1 billion. On July 2nd, it made $39 million. 5% of that is $1.9 million. So Disney and Marvel basically made less than 1% of the overall earnings the film made. Now, Disney and Marvel make bank off of the merchandising but that’s part of a separate deal.
The long and short is that it makes sense why Marvel and Disney would want to revisit and ask for more but they demanded too much and wouldn’t budge when Sony OBVIOUSLY said no. Granted, they offered to go 50/50 on everything so Sony wouldn’t be solely financing the movies and would share it with Marvel. Still, there’s no way Sony is just going to offer up 50% of their biggest franchise, that’s just stupid if they did.
Disney messed this all up. They kicked Spidey out of the MCU, Sony didn’t pull him. Sony wanted the current deal to keep going. Disney just got greedy and now we all lose