Also a difficult case to make. They're dominant because users have chosen to be a part of their network, and advertisers want to reach those users. It's difficult to argue they engaged in anti-competitive behavior by making a highly useful/effective product people choose to use. Up to this point, network effects can't be cited as anti-competitive. Looking at the times when Google did use their platform to bully other companies, it still wasn't in a business they dominate (Yelp comes to mind). It's difficult to argue an algorithm producing search results is inherently anti-competitive.