The first bullet was when Apple decided to monetize it and switched all new Macs to only get Hypercard Player instead of the full development stack.

They also didn't do a Windows port until it was way too late.

Apple also seemed to mostly stop development on it shortly after the System 7 release.

I think it was Apple's poor management and succession of ineffective CEOs in the late 80s and early 90s. They delayed bringing it to Windows, and lacked the vision to pursue adding networking features to it.

Eventually, Mosaic came along and the rest is history.