Disney made Spider-Man relevant again and Sony bought the studio that produced their hit game.
With Tom Holland and the director willing to continue working with Sony there was no downside for Sony to take on Disney with their own formula.
The average movie goer won't care if Spider-Man 3 is published by Disney or Sony. In fact, Sony won't have to wait around for Feige's planned cinematic universe to play out.
Won't surprise me if next we'll see a Spider-Man TV-series something in a deal between Sony and Netflix.
Disney made a really dumb move by handing Sony the candy store, not covering their behind and offering just a 50% cut when Sony can get the full 100% of the next billion dollar Spider-Man movie with the only downside being that Spider-Man won't be a cameo in a gazillion MCU movies that Sony doesn't earn a penny from.
I bet it was the executives in Japan that noticed that other than Kevin Feige's golden dick, Disney was holding 2's and they had a royal flush.