It’s true that Apple has done two moves to different chips with success, but both times it was to a more capable and probably powerful processor. When moving to PPC they allowed to run 68k apps/code without too much penalty. When moving to x86, there was Rosetta[0], that made the entire existing library /almost/ work seamlessly. moving to ARM... this might not necessarily be true. Sure, you have Catalina but iOS apps on macOS says nothing about all existing apps for macOS. I have no idea of the amount of already existing apps and what would be the amount of work needed to move them to ARM. Very likely Apple did the math and it will be easier/there will be incentives for devs to move to that platform. They do have experience though.