A lack of constraints mixed with a lack of real benefits.

Late-stage iPhoneOS was magical because of the constraints people were working with.

If you tell a developer, "Hey! Here's hardware with effectively no possible limits," they'll never write anything of value for it. A text editor and a way to do something you're already doing 5% faster.

If you tell a developer, "Hey! Here's hardware that's extremely slow and limited by today's standards, make something magical," they'll move the sun and stars to get you something that'll wow you.

Early-stage iOS was magical because of the new frontier offered; the constraints had mostly disappeared by then, but the ground was new and it presented what was effectively a new way to interface with the machine.