Can you connect the dots for me?
I'd recommend reading the emails. They show just how badly Sony needed Marvel's help to make a good Spiderman. Here's my favorite http://imgur.com/XiqC6fz
Edit: Also Sony was trying to make their own Spiderman universe instead of being part of the Marvel Cinematic Universe.
Disney has tried to get back as many as they could, and are continuing to do so. Off the top of my head, Universal currently owns theme park rights to Spiderman, Avengers, X-Men, and Fantastic Four on east-coast USA. In regards to film rights, Fox owns X-Men and Fantastic Four, and Sony owns Spiderman. One of the reasons Disney is pushing hard for acquiring Fox is to get back the X-Men rights from Fox, as that's the 'easiest' way to add them into the MCU.