Why is it a red flag?
How is it different from any other purely stylistic rules such as Strunk and White's prohibitions against split infinitives and the passive voice, which we've left far behind us? Why shouldn't people just write however feels natural to them as long as the message is clear?
Because LLMs use it constantly, to the point that it sets my teeth on edge and instantly makes me question if reading the piece is worth my time.