Why is profanity often based on bodily functions or God?

The point of profanity is to break social taboos to demonstrate intensity of emotion. Social taboos are real, so profanity has the desired effect of shock by messing with those taboos.

Most societies have strong taboos around religion. Most societies have taboos about excretion, and a lot of societies have taboos about sex.

The West doesn’t have these taboos anywhere nearly as strongly, and has replaced them with taboos around racism and sexism. So Westerners need some imagination, to imagine how forceful an impact profanity used to have.

Or, they need to substitute sexist and racist invective in their heads—although oddly enough, that’s not the same: prejudice singles out members of a community, rather than toying with the underpinnings of a community. On second thought, maybe that’s not so different after all.

In fact, there’s been profanity inflation, which is why Deadwood (TV series) had to use as obscene a language as they did. Cowboys swore plenty back in the day; but what they swore about broke taboos that just aren’t around anymore; so they’d sound silly today.

There was a time when not bloody likely scandalised a nation (Pygmalion (play)). And that time was way after the time of the Wild West.

(Btw, bloody is about God, not bodily functions. God’s blood.)