These are white label casinos. There are lots of them - some are totally free, some are cheap, some expensive.
The price usually depends on the degree of customization. If they just get a new front it is cheap, if it only lists the name of your choice it's free.
If they are customized with your name throughout, it costs.
There are major brand software casinos available as well as small brands and fly-by-night ones. Quality varies by the specific provider. Some can be respectable. Most are not.
Some you host on a server of your choice and buy a real domain for, most are hosted by the company and you just name them, no domain purchase - they reroute to you. (you need to trust them to do this).
There are thousands of them out there and most of them have never seen a single player.
You don't really "own" the casino - it just means that you are the only person promoting it (unless you get some affiliates to work for you). Since most of the people obtaining one of these casinos just want to "own" a casino and have no idea about how to promote it, they just sit there.
If you are good at promotion, you can make some money with these. The percentage of profits you get is somewhat higher than the usual affiliate percentage. But, on the other hand, if you are skilled anough to be successful with one of those, you can also ask affiliate programs for a raise of percentage and make the same money without the trouble.
Personally, I think they are a nuisance and too many of them are fly by night.