Good point. But, given frankly how many developers I know with Apple products, I suspect it may well be higher than you think. The main thing I like is flexibility: I have a home-built Kodi PVR with a TV tuner on a raspberry pi 4 in a neat little box. It works brilliantly, and also doubles as an adblocking nameserver, always-on reverse tunnel so I can access files stored at home remotely despite many layers of NAT, etc. There's no reason Apple's products couldn't do this.
But the main thing with Apple is that they manage the scope for life’s little bugs to creep into their UX by aggressively minimizing the number of things they attempt to do.
Think about how many times you unlock your phone, open the keyboard, open an app, etc, versus how many times you need to do something power-user-ish like running an adblocking nameserver, or any kind of server. They should spend money and brain-time optimizing the first things, first.
The latter is still important and cool but shouldn’t be doing it at all if they can’t slot it neatly into their smooth user experience.
As an investor I also don’t want them risking their super valuable brand and spending money developing fringe applications. You can buy a $50 RPi for that!
Why would Apple let you do it yourself when they can juice their services revenue by making you pay for the same functionality?