People wanted edgier content, stuff that felt more like real life. The bleap was a perfect solution in part because the bleap doesn't just erase a bad word, it also draws attention to it. Even while it is technically covering up the swear word, bleap, in my opinion, actually emphasizes it, underlines it, foregrounds it.
There's a particular one-kilohertz tone that is universally understood to be covering up inappropriate words on radio and TV. But there are other options, too, like silence -- so why did this particular *bleep* sound become ubiquitous?
Bleep!