I think usually it's just for fun. "Fook" is supposed to be evocative of Northern England in the same way "feck" is of Ireland, but in my experience no one in Northern England pronounces it that way for real. Not in the North West, at least.

People often write how they talk, and I find the best authors will incorporate dialect and intonation into their writing. One of my favorite examples is of Blood Meridian. It's so amazing that one can literally tell who is talking purely from word choice and grammar with no quotation marks and often no indicators of who is speaking.

I fucking think it's because they're fucking worried that fucking people on fucking Lemmy might be fucking offended by the fucking word fuck and its fucking derivatives. Let's fucking hope they fucking bookmark this fucking post and fucking come back to it in a few fucking weeks to see if anything's fucking happened to it. Fuck fuckity fuck fuck - fuck fuck.

I think it's use is popularized by the tv show 'Peaky Blinders' with the Birmingham pronunciation of the word.

Some have accustomed themselves of writing a bit more cautious, as multiple platforms have active swear detection (not the reason to use it on Lemmy, but there were are).

I thought it was to emphasize that they are Australian, but that's just because of a character in a book that I read.

Popular slang word they like, i guess? Not american here.