Why the heck would you use the phrase "Why the heck" in any circumstance other than to avoid censorship/algorithmic penality on a social media platform?
These things tend to get ingrained in you so you continue to use them even if you could technically use the words they replace.
Well, one good reason is that a person who generally doesn't "swear" can then choose to use them very effectively when the situation warrants. If you always go to strongest words when mild ones will do, you're out of things to say when you need to make a stronger/more forceful point.
I say "heck" instead of "hell" all the time. I'm not religious, so the invented "heck" is more of a swearword.