I disagree with you there.
Look at the little teaser at the end of ASM2 for Days of Future past. That confused a lot of people because they thought they meant the films were going to cross-over, when it reality it was some settlement that Sony agreed to so that Webb would direct the film.
I haven't seen ASM2, so I didn't know about that one.
As Marvel /Disney and FOX, that's a whole other kettle of fish. Word is FOX [quote=https://ca.movies.yahoo.com/blogs/wide-screen/does-disney-acquisition-lucasfilm-mean-marvel-film-universe-170451763.html]wasn't too happy[/quote] about Disney buying Lucasfilm, leaving FOX out in the cold.
It was probably easier for FOX and Sony to make a deal because Sony been on the financial ropes for a while. I would expect any negotiations between FOX and Disney/Marvel would have both sides playing hardball.