The cynical take is that they make a shit ton of money from services and Linux running on a MacBook won’t help them do that.
Yeah, and having the only supported OS be MacOS means they can entice people to upgrade when they want. No continuing on with 8+ year old hardware and a lightweight Linux distro even if it's fine for the intended use case.
They do also make a lot of money selling hardware, and as things stand today that business happens to make them look like the first tech giant to actually profit from the AI boom (because the hardware they've been developing internally for years happens to be among the best consumer-grade options for self-hosting LLMs). Making their hardware more attractive to tinkerers could be a winning move right now.
This, but also you would be allowing people to learn Linux. Developer with a Mac has to be one of the most common linux defectors. I suspect most people don't realize how doable and comfortable the switch can be.
The vast majority of people that buy Macs for the ecosystem aren't going to switch to Linux. That market will remain untouched. Outside of a few gamers who might want to put up with the x86-to-ARM translation layer and (for most A to AAA games) Proton to run some non-Mac games. And even they'll probably still dual-boot.
There's a portion of another market: people who want to run Linux and want a powerful laptop who buy x86 Laptops right now. Apple could expend very little relative effort while offering no official support by helping Asahi get that to a first class platform. They won't capture them in the ecosystem (and they never would have) but will still benefit from hardware sales to them.
Obviously, if they sold their hardware at a loss and subsidized that with ecosystem capture that would be a non-starter. But from everything we know, the hardware itself is very profitable.