I'm not the target audience, but I understand why some want it. For most Linux enthusiasts, any proprietary UNIX is a non-starter - they want full source code for everything.
To a degree.. I had the unfortunate privilege of breaking a 2568-day uptime of a Sun Fire X2200 1U server that was running Solaris x86 2.8 because our client changed their requirements that they could go to using RHEL for their webserver. While it could easily have run Linux (it was AMD Athlon X4), having it run Solaris meant that a lot didn't have to be compiled or source code needed, which meant that less time was spent trying to build the software that was to be maintained. It effectively ran itself, so I only had to patch the zone that was running inside it (like a VM), so the main core OS never had to be shut down.
The same could have been achieved with OpenSolaris, but Linux has the better support.
Even for those with a less dogmatic point of view, there's a bunch of things about Apple's UNIX which would be annoying or showstoppers for long-term Linux users. Apple's take on a lot of things is just weird to anyone who grew up on Linux. Apple ships creaky, ancient versions of many open source UNIX programs because their legal department decreed that Apple employees Shall Not Touch anything with the GPLv3 license. Lots of the apps Linux enthusiasts want to run can be (and have been) ported, using layers like XQuartz, but they'll always be weird and poorly integrated with the native Cocoa UI. Which isn't nearly as customizable as they window managers they're used to.
XQuartz comes in handy for me, just mainly for running an xterm. From there, and thanks to XCode, GCC (llvm, CLANG, etc.) can be installed to where I can compile anything I may need, which isn't much. If I wanted to, I could compile GnuPG and Mutt and have a way to send/receive mail and encrypt/sign any file I choose with my PGP key. But with having Apple Mail, Postbox, and a native GnuPG client for the Mac, I really don't need to. But the option is there if I want, as it does provide an ANSI C environment.
Once you accept that people exist who really won't run any desktop OS other than Linux, it's easy to see why there's demand for M1 Linux. What can you buy in x86 land which matches up with the M1 MacBook Air?
That is a fair point. The interesting thing to think about is what support Linux will have for the hardware, especially since it is a completely different architecture compared to what Linux can support (x86, sparc, ia64, alpha, s390, etc.).
BL.