IMO this is one of the things that fall into the “play well with others” rule introduced by PEP 600. Wheels can only make use of newer kernel features when the version is generally shipped by default by all popular musl-based distros, and once all major musl-based distros ship a certain kernel version by default, users that rely on older kernel versions are automatically removed from the coverage of a musllinux tag.
I am honestly not familiar with how popular musl-based distros handle their kernel version support, nor know how the “play well” rule is going to work out (since AFAIK no projects are currently distributing PEP 600 wheels yet). But I feel it’s probably better for the community as a whole if both glibc and musl distros can use this same rule so the experience learnt by either can advance things for both sides (and other libc implementations if they need their own platform tag one day).