I'm assuming someone else owned it, whenever I see that and all the "make an offer" links I move on and ignore it. Was the process easy?

I once registered web.site. I had it for a week or two before I tried pointing it at a server at which time someone noticed and took it off me.

This... isn't how domain registration works.

https://news.ycombinator.com/item?id=6397526

For the first few years, we used readme.io as our domain. When we did our Series A, I finally bought the .com for $170k. By that point I knew we were successful, and I figured the longer I waited the more it'd cost.

It's worth that much to any business that wants readme.com and believes it to be worth 170k. You don't need to be called Readme to want that domain. There are plenty of tech companies that want vanity domains to point to parts of their offering. I can easily imagine Microsoft, Jetbrains, Atlassian, or Replit making an offer for it.

That said, by far the most likely way any company would acquire it would be as part of acquiring Readme as a whole. If you want to exit by selling (rather than IPOing) the value of your assets still plays a small part.