With the wide use of containers, distributions such as Alpine Linux [alpine], have been gaining more popularity than ever. Many of them based on musl [musl], a different libc implementation from glibc, and therefore cannot use the existing manylinux platform tags. This means that Python package projects cannot deploy binary distributions on PyPI for them. Users of such projects demand build constraints from those projects, putting unnecessary burden on project maintainers.
Ref: https://www.python.org/dev/peps/pep-0656/