That's definitely not a case of a typo. From my understanding, the people who do that are trying to bypass textual swearing because for whatever reason, they don't want to be so "explicit" on sites like Facebook or whatever, despite the lack of any rules against swearing and such.
I say that this is rather dumb. I mean, I can understand if you'd like to keep a conversation family friendly by simply censoring swears, even though that's already oxymoronic in the first place, but it's essentially redundant to simply spell them another way to convey those particular words without actually saying them; that's still basically swearing at the end of the day.
And if it's not because of this...I guess people might do that because they think it's cool? Honestly, I think that in reality it's not.