It's a matter of priorities as well. There's hardly funding to prosecute everyone that breaks any sort of law. So you aim for the big fish. Many more are "hurt" by FB's practices than some random other small player. In that sense, FB is committing the larger crime.

But is in this case an EU institution selecting FB or a civil rights organization selecting the biggest offender? If the citizens complain about FB and going after justice why are you asking the citizens to find first other smaller and non US company that maybe did much less damage and start with them. Citizens should have the right to demand justice for illegal behavior of US company that makes business in EU without having the other camp calling protectionism.

It is like the Microsoft anti competition case would not take place until we find some small non US OS vendor to punish first so the Americans won't get upset.