[jstimpfle]

I didn't find it that hard. Just realize the different backgrounds and cultures that all these projects originate from. They all have their own ways of doing it.

man pages work pretty well for a lot of stuff that is POSIX. C interfaces and basic CLI programs you'll all find documented in man (with documentation beyond what is specified in POSIX).

The GNU folks have tried to push their info system, so maybe you'll find more details there for their commands. I guess most people use man because it's quick to access and a single page is easy to grep through. If that doesn't help, I'll just do a web search.