Much of why CM and other AOSP-derivative projects are popular is to get rid of carrier and OEM bloatware. Very few people don't install gapps, and while some of the gapps packagers (such as PA) now offer "micro" gapps packages with most of the unnecessary Google apps installed, the package recommended by CM (as in, linked from their wiki) is a complete one.
This is effectively Google's response to OEMs (especially Samsung) putting on atrocious crapware that was ruining the Android experience for many users. e.g. "this is why OEMs can't have nice things".
One of the biggest issues is that sometimes the OEM crapware would constantly hound you to create an account with the OEMs own ecosystem. Google's stuff, at least, usually doesn't hound you if you click "no" during the initial Google account setup. Samsung, on the other hand, would constantly spam me with persistent notifications until I rooted and removed their crap. Also, OEM/carrier crapware was far more likely to do funky stuff in the background without the user's knowledge/approval than GMS.