OK, but arguably Microsoft has more monopoly power than Facebook, Google and Apple, given its overwhelming market share. If you split up anything else, it's hard to justify not breaking up Microsoft.
The usual anti-trust argument for the last 30 (?) years has been about harm to consumers. Does the monopoly (or oligopoly) harm consumers or benefit them? If the latter, then regulators let the merger happen, or near-monopoly keep existing. It's hard to imagine a harm to consumers argument work in the case of Google or FB or Apple.
Look, I was militantly in favor of breaking up Microsoft in 1999-2000, the last trial. But the courts decided not to do so. The same rules need to apply to everyone. In that context I don't see any anti-trust effort happening, as much as it needs to.