Spider-Man - Homecoming and Spider-Man - Far From Home were HUGE money makers for Sony. Evidently Disney/Marvel Studios took a very minimal percentage of the profits of both films, but retained the licensing and merchandising rights, so they made a lot of $$$, too.
Some historical context about where Sony was when Spider-Man - Homecoming went into production is worth discussing. Because after the Sony hack of 2014 the studio was in a bit of trouble, including the head of the studio, Amy Pascal. She took a beating during that scandal. But the new Spider-Man movies really helped save the studio and her career, and I took note of her credit in "Far From Home" as a producer.
This issue is very clearly about one thing: MONEY. Disney wants a greater share of the profits. If you look at how MCU characters had been integrated into those two movies, it's pretty clear that bringing those characters into the Spider-Man films HELPED those projects. Especially if you're looking at the box office of those two movies compared with the Andrew Garfield films.
But Sony probably thinks they're in a strong negotiating position now. Their new Spider-Man movies have been successful at the box office. And two of the biggest stars in the MCU films have ended their runs - Iron Man and Captain America have both been written out of the series. Their absence makes Spider-Man far more valuable to the Marvel Cinematic Universe. While I think a lot of people have been surprised by the way some characters within the MCU have taken root (Guardians anyone?), is Marvel Studios going to bank on something like The Eternals that much?
My take? Sony and Marvel both need each other. Their continued success depends on them working together. Otherwise we're going to see history repeat itself as Sony will continue rebooting Spider-Man in order to retain the movie rights to the character. But I have a high degree of confidence that with the X-Men and Fantastic Four now back under Marvel Studios control they are actively working on a way to integrate those characters into the MCU, and we're going to see some great things from those segments of the Marvel universe.