Fuck as a mid-word addition

An infix is a word or component placed inside another word in order to alter its meaning. In English, prefixes and suffixes are common, but infixes are pretty rare. Some languages quite commonly use infixes.

Since the linguists have thought about this, they have come up with some linguistic rules that govern how you'd place "fucking" inside an English word. (This work is part of the study of prosody, which is the study of patterns of intonation and accent of speech, and how it affects meaning.)

• The fucking infix is nearly always placed before a stressed syllable. Thus we have "fan-fucking-tastic" but never "fanta-fucking-stic", and "abso-fucking-lutely" but not "ab-fucking-solutely". "Un-fucking-believable" is a counterexample that has seen lots of discussion -- the rule would dictate that we'd say "unbe-fucking-lievable", but nobody says that!
• The number of syllables in the base word is important -- there needs to be at least 3. It usually won't work with a 2-syllable word. An exception might be words that have two equally stressed syllables, like "sawhorse" -- "saw-fucking-horse". Although, when you'd have an opportunity to say that, I would never know. Two-syllable words with the accent on the first syllable probably never lend themselves to being augmented with an expletive infix. Consider "coffee", "dongle", "printer"... the infix would sound very awkward with these!

So why is Fucking an infix? Why did "fan-fucking-tastic" spring up in place of "fucking fantastic"? Throughout the rest of English, words are modified by adding things to their beginning or end; why should this situation be any different?

I think the answer lies (1) in fucking's role as a modifier for larger constructs like phrases -- it's usually inserted in the middle, not the beginning -- and (2) in the fact that when a single unattached word becomes a phrase in itself ("absolutely!") it feels natural to treat it as one ("absofuckinglutely!").

Okay, then: why did fucking's mid-phrase insertion rule spring up?

• Clarity. "Fucking" is not just an adjective but a verb (which is to say, a participle), and adding it to the beginning of a phrase can cause confusion. (There's a shirt sold in Japan, popular among those who don't like the patriarchy, that says, in English, I'm not fucking your baby.)
• Intensification. "Fucking" is, of course, a swear word and as such is naturally said at the most intense point in a phrase to propel it to greater heights. If we extrapolate for larger structures one of the placement rules vivid outlined above, it becomes "The fucking infix is nearly always placed before a stressed word", which fits nicely.