There are industries where one company has an effective monopoly, and others where the relevant players have tacitly/privately agreed to split or share the market. Competition is good for the consumer, but companies can usually make more money by forming business cartels and not competing with each other. Price fixing, market division, and bid rigging are all examples of this kind of collusion. These tactics are usually illegal, but they still happen regularly. Google any of those terms and you'll find lots of examples and related case-law, and those are just the times companies did it so egregiously that they got caught.

Companies collectively agreeing not to pay for a patent, and all profiting when it becomes public domain soon after, would just be a variation-on/extension-to price fixing and market division. The inventor would usually not have the resources to pursue legal action and would have a hard time proving that the companies involved didn't just think that licensing the patent was a bad investment at the time.

Also, just to clarify, "solo inventor" here really applies to any entity/organization that is tiny compared to the companies it's trying to licensee its patents to.