This is definitely the case with cover letters for jib applications. The ones written by GPT appear to be pretty obvious - my guesses could be wrong, but after seeing most applications not having a cover letter for years to most applications having one over the past few months, I suspect GPT is involved, and there's a distinct 'style' that seems to be showing up.
Using GPT could be the 'bootstrap ui' of product announcements. It looks great on its own, but put it next to a bunch of other companies and they all fail to stand out.