68k gave way to PPC because of limitations in the family.
PPC gave way to Intel because a powerful enough laptop chip was not on the schedule.
OS 9 and below are not robust secure operating systems and Apple does not have infinite resources despite it's address.
Apple does not force developers, however it does strongly recommend that developers spend their energies on more modern operating systems.
For example I am writing a Web Browser for System 6, Apple have not shown up at the door and dragged me away to Gitmo, infact they did the opposite and let me register a unique creator code for the application.
As a direct comparison, Microsoft NT 4 does not support USB, do I run around screaming blue murder? No, I run Windows 2000 which does support what I want.