There are few threads about this. I have not seen a conclusive reason why this is happening. And it is happening to a lot of people. Including me.
It's probably a way of abusing google to circumvent the cloudflare protection and try doing a ddos attack.
Do you regularly have hits from google and other search engines? Because most of the projects that are in those threads do not seem like the kind of games and assets that get searched by name via google, but would rather get hits from within Itch.