American law tends to center around harm to consumers. By that reasoning, it can be hard to prove a market with a single player is actually anticompetitive if that player isn't muscling out better options for consumers from the space (i.e. if they corner 90% of the market because they really do offer the best value at the lowest price, who cares).
European laws tend to center around the philosophical core that the market should be a level playing field for producers or vendors, so even if all other choices than the dominant player are worse for consumers, the market needs to stay competitive so that business firms don't die and put a bunch of people out of jobs.
It's useful to know where someone is coming from in considering topics like this.