I don't think you could break them up in any meaningful way. What would you break Apple up into? The company that makes iPhones and the company that makes iPads?

Or Facebook? Two social networks that get half of the population each?

Breakups only make sense for vertically integrated companies. I guess you could break up Google (it's already done so itself to some extent with the Alphabet reorg) but not in a way that's meaningful, other than maybe requiring advertising to be its own company.

Also it neglects the fact that their biggest asset is their domain name. Google.com might be worth literally trillions of dollars. How do you break that up?

If anything, I'd argue the government could regulate Facebook since it's basically a natural monopoly, much the way it does the NFL or basic utilities.