Earlier quoted context omitted.
I am speaking entirely speculatively, but I’d imagine it might be having to do with going for low-hanging fruit, or at least trying to chip away legally before (or instead of) sweeping anti-trust litigation. The appetite for this kind of action hasn’t exactly been great the last few decades, and big swings can lead to big misses (like Activision-Microsoft)
Lina Khan has great intentions but poor results. None of her big tech trials have been successful. EU seems to have a better track record reigning big tech than US DOJ.
The EU also has a much stronger regulatory framework than the United States does. American corporate-friendly policy decisions make litigating anti-trust more difficult. Not to mention congressional inaction means regulatory policy is stuck generally in the last century. The case against Google has seemed the strongest yet, but we shall see how things play out.