Imagine going to work or a social meeting where everyone looks and sounds the same(or just a limited set) all with the same perfect tone, body language and communication style. Sounds like a nightmare and I would find it hard to relate and get that "perspective", when there is nothing to differentiate a person.

I guess everyone using LLMs for text is similar to that. If everyone uses the same LLM style, its hard to understand where the other person is coming from. This is not a problem for technical and precise communication though(the choice of LLMs in that context has other risks).

It is also strictly not an LLM capability problem because they can mimic or retain the original style and just "polish" with enough hints but that takes time, investment and people go through path of least resistance. So, we all end up with similar text with typical AI-isms.

There are other reasons to dislike LLM text like padding and effort asymmetry that have been discussed here enough.