Antitrust doesn't care about the market share, it cares about actions taken to restrain competition. Government-granted monopolies (e.g. copyright law) have partial antitrust carve-outs: I can't sue Disney for owning the copyright over their own films[0] even though that's extremely anti-competitive. Apple was savvy and couched their defense around their ownership of iOS: i.e. "you can't tell us how we sell our OS". Google could not avail themselves of that argument in the Epic case because they had explicitly open-sourced Android.
But that's not the biggest problem. The Google lawsuit is unique in that not only did a lot of Google's own internal e-mails basically spell out exactly what crimes they were committing, but they also got caught spoliating evidence[1] by aggressively pushing relevant persons in the company to turn off chat history and recording functionality that was legally required to be enabled. In contrast, most of the decision making at Apple was "whatever Jobs thought was best" and people just did what he said. You can't subpoena a corpse. And while there were internal tech emails discovered in the Apple case, none of them were as damning as the Google ones, at least by the standards of a legal system that considers monopolies to be OK as long as you can pretend to be a starving artist.
As for games consoles, the argument[2] is that consoles are special-purpose devices while iPhones are computers. I personally disagree with this, consoles have "apps" now just like phones and they have the exact same positioning that allows them to gain supra-competitive profits like Apple does.
[0] More peripheral claims, such as having a monopoly over theatrical distribution, can and have give rise to an antitrust lawsuit. You have to prove that the market power they are using is above and beyond the market power the government intended them to use.
[1] "spoliate" as in, illegally destroy evidence relevant to ongoing litigation.
[2] Provided by Epic, oddly enough. I know they argued it to try and narrow down Apple's market definition, but I also suspect that was to avoid console manufacturers asserting some kind of universal default[3] / reverse class solidarity move and pulling Fortnite off PSN/Xbox/eShop until Epic drops the Apple lawsuit.
[3] Universal default is a clause added to loans that says that defaulting on any other loan defaults on this loan, too.