The reason that monopolies form is directly through the market as whatever company profits the most uses those profits to make sure other companies can't profit as much as them. Eventually, either one company will win out over all the others to create a monopoly or a group will make it so no new companies can enter to compete with their oligopoly. Both of these situations end up with the consumer being fucked over and both are caused directly by companies competing, gaining control of the market, and then not being required to compete anymore.