Why is it bizarre? Google has near-monopoly market share in search and in ads and Apple is the only thing standing between them and a monopoly on the browser. Furthermore, they've demonstrated anti-competitive behavior in all three markets.

The only market where Apple has a monopoly is the marketplace that they created for themselves, and a high profile case already tried and failed to use that definition of the market to argue antitrust. The DOJ is trying again anyway, but it made perfect sense for them to wait until Epic vs Apple was decided before starting work—why waste time on something that could be moot by the time they finish?