What is making you think that monopolies can only occur with government action? The first utility to service a region is a de-facto monopoly. I also gave two examples already of ways monopolies have occurred without government intervention: anti-competitive behavior and barriers to entry. Monopolies without government intervention are common enough that there’s a term for it: Natural Monopoly https://www.investopedia.com/terms/n/natural_monopoly.asp

That article gives more examples of ways monopolies occur without government intervention, such as mergers and takeovers, and collusion and price fixing. All of these things have happened multiple times in the past, so history provides all the proof we need that lobbying or other government assistance is not required for monopolies to form.