It would be feasible to upgrade if you were incentivized to make it work. It sounds like some programs, particular Adobe which changed its licensing model, are not incentivized to make it work.
This is fine for the producer, who can drop support for old software. It's not fine for the consumer, who may not want to pay yearly for their software and therefore don't want to upgrade to the latest versions.
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Don't worry, I'd feel differently if I held Adobe stock
What about legacy applications which are no longer actively developed? I still use Aperture quite happily, and there's no obvious alternative (aside from Lightroom which has a subscription model).
I don't see why Apple couldn't provide an optional compatibility solution, even if it were something I had to download separately.
If you were already using Cocoa, and were heeding deprecation warnings for the last 10 years, there should be zero issues.
Of course, with lots of software (especially projects started decades ago) it might have been difficult to do this. But the only paths forward were
(A) expect to drop support once 32-bit was removed
(B) gradually replace components which were dependent on things without 64-bit versions
(C) wait until 32-bit support was removed, then have a terrible time updating
And the writing on the wall has been there for a very, very long time.