https://www.wsj.com/articles/the-antitrust-case-against-face...
The main takeaway I got was that they have different views on what is a monopoly and how/when it is bad. From the article:
> The different outcomes hinge in part on different approaches. European regulators are more likely to see a shrinking pool of competitors as inherently bad for both competition and consumers. American regulators are more open to the possibility that it could be natural and benign.