Earlier quoted context omitted.
By Linux do you mean GNU? Because those are the wordiest and least straightforward. BSDs tend to have excellent documentation as do some individual projects (git), while others (OpenSSL) leave something to be desired. And of course GNU tar is a special little hell. But Linux just happens to run on a GNU userland most of the time so you get those a lot.
On many Linux systems there are likely to be more non-GNU commands than GNU commands, so I'm not sure your argument fully works here. GNU historically never made man pages: they used Texinfo for documentation, possibly combined with a tool to convert Texinfo to man pages. That shows in the result: an entire manual all joined together in a single unreadably long manual page. The bash man page is a nice example of that…
Many GNU manpages are generated with help2man, which causes the opposite problem, i.e. they are too terse. (Also, their typographical quality is often low.)