Keep in mind that Apple is constantly making big changes to their OS which makes things difficult for other developers. The AU wrapper in the current VST3 SDK works better, but it’s impractical to recompile old plugins that have long been superseded. Doing that would inevitably break things, and the time they would spend fixing them would be better spent making the next version better.
Don’t delude yourself thinking that these Logic updates are truly “free”. You’re paying for them and much more the moment you buy a Mac, which costs almost twice as much as a custom built PC… And you’re probably buying a new one every few years.