Over the course of three movies (Spiderman 3, ASM1, and ASM2), Sony burned up all of the goodwill Sam Raimi had built up for them.
Kevin Feige apparently made the first Sony deal very one-sided in Sony's favor in order to make the deal happen, to show what Marvel Studios could do for Sony. Feige used Sony's money to make two MCU Spidey movies for Sony and gave Sony all the profits (in exchange for cameo appearances, which didn't have much value for Disney but really helped to sell the illusion), and put Spiderman back on top.
AND Sony was still able to do their own thing and make movies like Into the Spiderverse (which is great), while loaning Tom Holland to the MCU.
And then Disney asked to be made an equal partner on the MCU Spiderman films, instead of just handing Sony $1 billion movies (aka the largest movie Sony has ever seen) for free. 50% risk, 50% reward. Yeah, Sony's only getting half the profits, but they're only putting up half the money. And Disney supposedly offered to increase the flow of movies to make up the difference. That's diversification, and it means good business.
Sony could have countered by asking for a piece of the boosted merchandise sales (since Disney seems to be winning more than Sony in a straight 50/50 deal), or asked for a percentage of the box office from the MCU movies that include Spiderman cameos, but something like the "50% merch sales" that people tossed around is groundless and ridiculous. Unless Sony has something they can offer Disney on the merch side of things (Sony clearly doesn't).
Sony made a bad move by letting this deal die, and it doesn't really affect Disney, because Disney doesn't need Spiderman (it's just the fans and Kevin Feige who want him). But this is the second time Sony has killed a good thing they had going with Spiderman, so it's not surprising. The real surprise is Sony fans insisting that there's no way Sony will fuck Spiderman up a third time.