1. Failed product market fit. These will be for sale, but you won't want to buy them because operating them will cost more than the revenue they produce.
2. The market likes the product. In this case, the original owner can just hire people to do the work, so there's no reason to sell.
1. Sure, bad businesses exist. When they do, they're priced accordingly or just can't find a buyer.
2. It's called an exit for a reason. There are million reasons to exit (eg: Big life event, wanting to cash out and invest elsewhere, bored of the business, have other projects, etc, etc, etc.)
Just because someone is selling a business does not mean it's a bad business. I say this as someone who acquires and grows online (e-com) businesses as my primary wealth vehicle.
I had no idea you were on Hacker News, TJ, what a welcome surprise
Lots of people also sell good SaaS products because they have others that have taken off (I bought one last year from someone who got funding from YC on another project, for example).
"The market likes the product. In this case, the original owner can just hire people to do the work, so there's no reason to sell." is also flawed. Do you have any idea how many developers/creators hate the idea (and reality) of hiring and managing people? Plenty would prefer to cash in and go back to building and let someone else build a team.
Have been guilty of this myself and seen so many overconfident devs who think they can manage it once they "get there" despite the entirely different skillset that's required for the role. Someone who can do both at the same time is incredibly rare.