A better question might be: what hinders this process today? Capital disparity plays a role (a wealthy company can perhaps make a competitor a buyout offer they can't refuse, or temporarily lower prices to try to kill them), but another major cause is excess regulation and the weaponization of intellectual property.
So they sell the stock of the company that is wringing out excess profits just as they are putting money into the “disruptor” that is going to capture all the consumers leaving company #1.
Now ensure that you push for a decade of overleveraged growth and regulatory capture (ensuring you don’t get diluted the same as the founders) and now you have shares of an entrenched quasi-monopoly - your task again now is to demand margin increases and stock buybacks in order to exit your position and buy your name on the local college library.
Wash rinse repeat all while taking money/risk off the table personally each round so when it collapses finally and the companies are finally ground into dust, you and your family have long exited and are onto the next thing.
For example, if Amazon has a monopoly, why haven't capitalist profiteers bled it dry yet,
And then the winner just lowers them, now what?
The answer is the former then we should remove governmental barriers to competition. If competitors can't theoretically undercut the price, then it's hard to see how more competition would favor the buyers. Surely they're not better off with 10 competitors at Double the price.
Last, there is the issue of time. Competition doesn't happen overnight
A reason why a new competitor might not be able to compete on price is because of capital disparity. The winner can lower prices, buyout the competitor or if that fails they can always turn to buying out distributors/suppliers/key employees of their competitor
The economy must go in growth/bust cycles, where growth brings out new ideas, and bust cleans up the inefficiency. And keeping it decentralized keeps busts manageable.
But if you instead let everyone merge during good times, and then bail them out during bad times, the next good times will never happen - the incentives are all wrong!