[throwaway7356]

Most distributions also don't allow to 'customize' any of the following:

- compiler used for building the distribution, - libc implementation, - C++ standard library implementation, - coreutils implementation, - system shell, - kernel (e.g., using Hurd), - PAM or equivalent, - util-linux, - package manager,

and so on. systemd is just one more thing in that looong, looong list.

[jcgl]

And has a lot more practical benefit than any competing implementation of, say, your libc or coreutils.