Why expired domains are very costly?

[lemon_1800]

Dear lemon, some expired domain have already popular, also get visitors, so their cost is high.

Thank you.
I want to know because the domain names are so costly, does that mean they are selling website also along with the domain names? That's why I think it's costly.
Basically, they are mentioning they are selling domains, but in fact, I think, they are selling websites also along with the domains. Am I correct?

I can see some domain names are as much as $2,000 or $3,000. So it must be a website, and domain alone.