Many studios and many musicians are not wealthy enough to throw out a roomful of working equipment just because it doesn't conform to industry trends.
The low-level interfaces in question were changed almost 4 major versions back. There aren't any new interfaces or APIs that haven't existed for 6+ years already. The only people complaining are the ones that procrastinated because Apple continued to support their outdated apps.
If everyone should have been prepared because this change has been in the works for so long, then surely it's inexcusable for Apple to have left the new stuff in a poorly documented state all that time. If you do feel that Apple's lack of preparation is reasonable when they had even more warning than third parties did, then it seems unreasonable to fault developers for also not being prepared.