If an author has "no original ideas", does that mean they are just bad at coming up with them?

It could mean a variety of things: they can’t come up any similar ideas, they can’t think of ‘workable’ ideas, yet, or even more likely? It’s now been so long, the pressure for a follow-up has dropped significantly, thus lowering their next book’s success.

Also, it’s not uncommon to develop a reputation for a single genre, yet have no experience or little awareness of others. So, if their newer work flopped, that’s more a matter of not doing their due diligence, and similarly nou successfully advertising, promoting or ‘selling’ it to the public.