It actually is as simple as the OP said.
That was the main reason why Apple went for Imagination instead of ARM or Qualcomm when it comes to mobile GPUs.
Imagination market cap has been falling hard in the latest years, so hard to the point that their only customer until now was Apple. They were desperate and they signed very risky deals in order to keep Apple as a customer.
And Apple is a complete control freak when it comes to their products, the idea of not being able to control the stuff they put on their products is unthinkable to them.
So Imagination signed a bunch of architectural deals (instead of purely implementation deals) because that was the real product Apple was looking for.
Don't let yourself be mistaken, this whole situation is far from a surprise to Imagination. They knew this day would come, they were just trying to cling on to the little market they could find until they found another deal in order to stay afloat.
