For this "LLM style were already the most popular, that's how LLM works, then how come LLM style is so weird and annoying" I have 2 theories.

First, LLM style did not even exist, it's a match of several different styles, choice of words and phrases.

Second, LLM has turned a weak plurality into a 100% exclusivity.

Say, there are 20 different choices to say the same thing. They are more or less evenly distributed, one of them is a slightly more common. LLM chooses the most common one. This means that

   situation before : 20 options,  5% frequency each
   situation now    :  1 option, 100% frequency

LLM text is both reducing the variety and increases the absolute frequency drastically.

I think these 2 theory explains how can LLM both sound bad, and "be the most common stye, how humans always talked" (it isn't).

Also, if the second theory is true, that is, LLM style is not very frequent among humans, that means that if you see someone on the internet that talks like an LLM, he probably is one.