They can’t and this is by design

You need capital and increasing amounts as you get closer to threatening any monopoly. Who do you think have that capital? People that want to end monopolies? No they want to just be part of a new one. So unless you’re just offering a new monopoly opportunity they won’t see the value and you’ll not even start.

Don’t forget, you don’t accidentally become a monopoly, the govt protects you. So beyond a certain point, you start dealing with government impeding you on behalf of corporations you’re affecting

In my opinion the only way to end this process without just making a new set of monopolies is with non-stock cooperatives but it’s going to be a long road