I don't think this lesson is getting lost accidentally, but intentionally. There was a brief moment in the late 00's/early 10's where companies were creating these rich web API's that would let you (and other services acting on your behalf) interact with their system in arbitrary and novel ways. But that turned out to not be very profitable (or at the very least, wouldn't let you create a walled garden that would get 100x exit for your VC's) so we've steadily moved to more locked down, less interactive, less open, less useful, but ultimately more profitable services.

Emblematic of this journey is Twitter, I think.