Without market restrictions, smaller competitors have a stronger chance of breaking into a market and decentralizing the industry. However, dominance by a majority party tends to be the natural order of things. Case in point: the crypto market, how Bitcoin has maintained 50%+ dominance for most of the industry's history while many competitors fight to split the other half.
I think the drive for competition comes from a natural desire for choice, or at least the illusion of it. Also, geographic concerns tend to lead to some level of competition due to time factors. As humanity expands beyond the Earth's atmosphere, the distance and time required to organize a monopolizing cartel becomes more difficult. This is the same effect that led to the American Revolution, where the central authority was just too far away to be entirely efficient.