In light of competition being the missing ingredient, the question becomes how does one maintain ongoing competition in a system where the bigger of two competitors tends to win and the winner of two competitors tends to get bigger? That's exactly what happened here: Facebook was bigger than WhatsApp, and FB+WA is bigger than Insta, so FB+WA+Insta is a lot bigger than anyone else.

Back in the day when Microsoft was the one in the DoJ's sights someone compared it to a dog race. Dogs don't have jockeys, so you have to figure out some other way to induce them to run. The way most tracks (probably all, idk much about dog racing but it's a useful metaphor here) do that is by having a mechanical bunny that runs out ahead of the dogs and activates their prey drive. The bunny has to be ahead of the dogs, but not so far ahead that they don't think they can catch it and give up. That means that every once in a while a dog will get the timing just right, go extra hard, and actually catch the bunny. At that point, the race is over for everyone until someone steps in to shake the dog loose from the bunny and give everyone a reason to run again. Our system is like that: we have to encourage everyone to do everything they can to catch the bunny but also ensure that they never actually do. Bill Gates was the first person in my memory to catch the bunny, and needed to be shaken loose. Now it's Zuckerberg, and probably Google, that need to be pried off of their respective bunnies so that everyone else has something to chase.

For a start, and it might even be enough, you strictly enforce anti-trust laws which are already on the books that prevent sufficiently large firms from acquiring their competitors and doing exclusivity deals. These laws have largely been ignored for decades and I don't know what to call that other than blatant corruption of our government, but it's slowly starting to change, in a bipartisan way.

Microsoft escaped the worst of what the government wanted to do to them for their anti-trust violations. It may not go so well for Google as they hold the distinction of being the only company in US history to have been tried and found guilty in three separate cases of possessing three illegal monopolies all at the same time. Two example measures under discussion in the court at the moment are forbidding any renewal of their browser default deal with Apple, and forcing them to sell off Chrome. We will see soon enough what comes next.

Foreign competitors is how you get competition usually. The big 3 auto companies can lobby Congress and discourage competition. When American Cars started installing tailfins (purely cosmetics) instead of competing on fuel performance, maintenance or price, they were opening the door for the Japanese auto industry to eventually take over, with the crisis of the oil shock being the instigating factor for people changing their consumption habits