The government, in the US at least, is more powerful in matters of life and death, i.e. militarily. That doesn't make it right or fair to use that power. Not even the democratic will of the people makes it fair to simply break up a company.

Why is it fair or unfair to break up these companies? The government should be powerful isn't a reason.

I'll start: it's not protecting the consumer from monopoly prices. Google and Facebook don't charge the primary "consumer" anything, and ads are cheap. Amazon has competition (Walmart, Target). Apple has competition.

What might be fair is using the democratic will of the people (although this is really just something done by representatives who can be influenced and don't always act on our will) to pass laws specifying behavior of these companies as illegal. Actual behavior, things like collecting gigabytes of personal data per individual to target ads, not things like "having too much money." The companies are not outright destroyed if they can find a way to make money without leaning on that behavior.

Except for the notion of inalienable individual rights. One of the hallmarks of the US form of democracy is that government is NOT the greatest power. Its power is limited and must protect the individual rights of its constituents (people and states in some contexts).