A good point. "Famous author" is a marketing term for Grammarly here; it's easy to conceive of an "author" as being an individual that we associate with a finite set of published works, all of which contain data.

But authors have not done this work alone. Grammarly is not going to sell "get advice from the editorial team at Vintage" or "Grammarly requires your wife to type the thing out first, though"

I'll also note that no human would probably want advice from the living versions of the author themselves.