Iv seen posts with people substituting rape with r@pe. Other than bypassing filters I can’t see a reason to censor just 1 letter that doesn’t actually censor the word? I see if you fully censor the word, but even still context completely ruins the censorship.
My understanding is that content creators have figured out which words trigger demonetisation of their videos (and to a lesser extent other content) so they’ve bowdlerised what they say to get around this. Other people presumably picked that up and used it.