Apple has the ability to both support i386 software on x86 machines, and choose to not emulate that software on future ARM machines. If your supposition is correct, Apple is effectively crippling their current products in order to make their future products seem less bad by comparison. That's horrible.
And in the process, Apple is asking developers to rewrite i386 code for an amd64 architecture which they ultimately intend to abandon anyway.
Maybe. Maybe? I doubt they're motivated by malice or laziness, but nobody in this thread can say one way or the other. What I can say with high confidence is that unless we're in the meeting room at Apple we can only speculate based on little to no hard information. It's entirely possible that there are sound engineering reasons behind what they've done.
AMD64 is going to be around for a very long time; any developer that is having difficulty migrating code from i386 has more fundamental problems than Catalina.
And in the process, Apple is asking developers to rewrite i386 code for an amd64 architecture which they ultimately intend to abandon anyway.