Someone could start a website and build data centers but google and others would block searches, comments about new competitor, agreements with other sites not to use their search. The article below was longer earlier in the day but is now a snippet of what I saw.
Google had agreements blocking competitors
https://www.fastcompany.com/90322678/google-hit-with-another-eu-antitrust-fine-the-grand-total-now-comes-to-e8-2b
Google didn’t allow its AdSense customers to feature rival search engines on their sites.
Another article about fine
https://www.nytimes.com/2019/03/20/business/google-fine-european-union.html
Google is another story. I was strictly speaking about Facebook.