From another point of view, looking at the government as an institution rather than through its role as an advocate of the people, you could also make the case

From another point of view, looking at the government as an institution rather than through its role as an advocate of the people, you could also make the case that the government should oppose any massive consolidation of wealth/power as a threat to its own power. FAANG companies each individually have higher annual revenue than most countries' GDPs. In the absence of government intervention, there wouldn't be much to stop them from turning into British East India Companies and establishing banana republics, raising private armies, etc. In an extreme scenario, some kind of corporate Genghis Khan could hypothetically consolidate the S&P 500 into a single megacorp if the DOJ allowed it to happen, and that company's revenue would be about half the US GDP (making it the third largest "economy" in the world). It would effectively be a hostile state right in our own backyard. Would we even have the ability to enforce taxation if they said no? What would stop them from wielding that incredible wealth to effectively buy a majority stake in government?