Sometimes it is the best choice of words. Most people who swear are not using the traditional bodily or religious connotations of the words, they are using them for emphasis or exclamation. Those uses are so much more common than the original meanings that outside of specific contexts, the new emphatic meanings are the default.

When referring to the original meanings, I think it is very vulgar to use those words, for instance saying "Take a s---" or "f------ your girlfriend". Those make me cringe. But those same words still work for me as exclamation, as in "S---! I lost my wallet!" or "His house is so f------ huge!".

I think that swear words are useful in this context because the social norms against using them keep them relatively scarce, which gives them value. When marketers have overhyped everything ("Extreme Toothpaste! The Ultimate Chili Dog! The Greatest Athlete Ever!"), the scarcely used swear words are valuable for conveying meaning because everything else is cheapened. If you could buy "Whitest F------ Teeth" toothpaste, swear words would not convey any additional meaning and would probably be used less.