Of course they lead to monopolies. If you start with a large number of equally capable suppliers and one somehow gains an edge then that one will be more profitable than the rest allowing it to invest and reduce its costs. This makes it even more competitive and provides a positive feedback loop. Eventually its competitors go bankrupt or get bought out by it.

Regulation can certainly exacerbate the problem, for instance rules that have a fixed annual cost or where the costs do not increase in line with volume favour larger concerns.

The idea that a totally free market can exist is a fantasy based on assumptions that simply cannot hold water. Regulation is necessary in order to prevent the powerful from abusing the weak. The fact that there are poor regulations does not invalidate the concept.