Apple went out of their way to add support for third party OSes to Macs. They actively made tools to allow the Asahi Linux folks and others to boot unsigned OSes on M1 Macs. They would have had much less work - both in terms of making and maintaining the tools as well as customer support work - if they kept the boot system more similar to the iPad boot system it derives from. In general really Apple doesn't seem to be interested in closing down the Mac at this level. Hence why you can (attempt to) run third party OSes on virtually all Macintoshes going back to 1987 [1].
I for one am happy with that. If I buy an Apple Silicon Mac, I won't be running Linux on it - at least not on bare metal. But I might do that in 10 years after Apple's support has ended.
[1]: NetBSD claims to still support the Mac II, a Motorola 68030 based Mac release in March 1987: https://wiki.netbsd.org/ports/mac68k/
I wish there were sleek, metal body lightweight laptops with Linux (w/o Windows hence minus some cost) which just worked out of the box (one that didn’t require hunting around forums to have basic functionalities), but there isn’t. And no I don’t mean that one or two exotic OEM/model. But a general availability.
So people for whom cost isn’t a concern they buy Macs.
In general, it's because they get out of the user's way and it becomes invisible to the user's workflow. Linux always involves tweaking the system just to get work done. The integration of the software and hardware of the Mac is why the user experience is no competition.