Their excuse is this is a feature that benefits Apple more than them. Apple caused a lot of extra last minute work and probably unhappy app customers by not giving developers a week with the golden OS version for testing and bug fixes, which is what they usually had. So developers made their apps work, but don’t feel a lot of need to add the extra features in any particular hurry.
I write industrial machine code. Customers who do similar things get the immediate (as possible) fix to get them back to the features they had, but integrating new stuff gets pushed off while we A) make sure that the patches work and don’t have a problem that isn’t immediately apparent and B) adding those features doesn’t break the system again, requiring someone to reload an uncorrupted version of the last stable code and then reinstalling the new code/features. It is isn’t as simple as just throwing code together and doing an update when you didn’t have even a day or two for problems.