> I'm not aware of how regulation of competitive markets would lead to monopoly

Competitive markets will always tend toward monopoly because that is the state at which the highest profits can be extracted. Regulation can, in some cases, help push it a bit faster in that direction by making barriers to enter the market even more onerous and expensive thus limiting or even eliminating new competitors. This allows the existing large competitors to either continue to knock out or buy up smaller ones, and the few remaining large ones to either merge to a single entity or settle into a state of non-competitive action (effectively collusion) where the market then either is or behaves as a monopoly.