You can to some degree with Cloudflare and other solutions. But, do you want to block them all? AI is a very useful tool for people to discover information and summarize results. Especially in scholarly publishing where one would have to previously search on dumb keywords, and have to read loads of abstracts to find the research that pertains to their interests. So by blocking AI crawlers and bots completely, you are shutting off what will probably end up being the primary way people use your resource not too long from now. arXiv is a hub of research, and their mission is to make that research freely available to the world.