• There were other sources of fur on the market. Not a monopoly.
• Not familiar with the New River Company, but color me highly skeptical that this was a genuine market operator with no protections or privileges. If you have a good account of it, I'd be interested to see it. The network effects and high infrastructure costs make utilities especially interesting.
• Standard Oil's market share had begun declining before the Sherman Act passed (https://mises.org/mises-daily/truth-about-robber-barons) and they weren't charging elevated prices anyway. The large market share came from innovation and offering lower prices than others could match. It took a while for competitors to catch up.
• I thought DeBeers did have state-granted monopoly protections. Plus, there are other sources of diamonds, including artificial ones, so the market was pushing towards competition, anyway.
• Not familiar with ASML situation.

So, not even the cherry-picked examples form the pattern you describe. I maintain my "almost always" position. Monopolies are hard to maintain because they create the conditions for their own demise: elevated profits. That is the self-correcting mechanism that you say doesn't exist.