At Apple, the amount of debate, code review delays, and interdepartmental meetings made everything take forever. I once waited 2 months for a code review there. A feature I wrote and pushed for Leopard didn’t actually ship until Lion.
Back then there was severe priority inversion, anything the desktop needed got delayed by iOS priorities but also the senior engineers with magic rubber stamp powers were working on iOS. So changes for the desktop stack never got approved without significant and needless delays.
Being less than 10% of $260b in sales doesn't excuse neglecting the product. Also maybe their Mac sales would be higher if they hadn't destroyed their laptop by replacing the function keys with a touchbar.
It also means, if a critical mass hate developing on Macs, then iOS software will suffer. App store fees are already a business pain point for app developers. And web browsers are getting capable enough now that it's probably feasible for a lot of apps to go back to being browser only.
It's going to be hard to reverse a trend away from Apple if it starts. Imagine what would happen if Microsoft Visual Studio becomes the IDE of choice for iOS development after devs ditch macOS in droves. Microsoft won't play nice.
Apple isn't watching their flanks by letting macOS atrophy and a competitor will step in if they don't cover it.
You act like developers have a choice. Companies go where the money is and developers do what companies tell them. The supremacy of the indie developer died a decade ago.
There are very few apps that could be web only apps that are making money via in app purchases. Most of the money being made in the App Store are pay to win games. Most of the subscriptions apps that use to allow in app purchases are already forcing users to pay outside of the App Store - including Netflix and Spotify.
Back then there was severe priority inversion, anything the desktop needed got delayed by iOS priorities but also the senior engineers with magic rubber stamp powers were working on iOS. So changes for the desktop stack never got approved without significant and needless delays.