This makes it literally impossible for anyone to make a competing search engine because millions of doors are slammed in their face. There is no practical way to negotiate access at this scale either leaving no options for small startups — e.g.: AI-based search!
One possible anti-monopoly measure would be to force Google to mask the identity of their bots. E.g.: force them to use a random IP address pool that third parties can also use without their permission.
IMHO breaking up corporations is a bit heavy-handed and not the only remedy available.