Oh c'mon, people rarely wrote down bawdy songs (particularly when most people could hardly write); they just sang them, and others learned them that way. The only printed records we have of most songs, prior to the recording era, are broadsides and songbooks, where songs were routinely expurgated even when dealing with salacious situations.

And consider the situation of the average cowboy: a hormone-riddled guy in his teens to mid-20s stuck out on the range or ranch with hardly any women available, lots of time to think about them, and a need to build himself up to the other guys. Of course songs like this were plenty filthy!