Bait and Switch would be one way. The founders probably wouldn't want to sell to someone doing that though.

I'd buy the domain name, but I suspect it will go for a lot more than $1000.

If they were trying to sell the whole package, including the domain name, which is required for the service to continue supporting all the existing links, and no one would buy it even "for a token amount", then why would the domain name alone go for more than that?

Because the domain doesn't cost anything to maintain. The service has hosting and bandwidth costs, which must be relatively substantial for a service of their scale.

Because I think "a token amount" is (much) more than $1000 for a business. As it is for a short and readable domain name.

Domain name alone is more valuable than whole package with a requirement to keep the service running

Frankly, I don't know right now, but $1000 seems to be obscenely low for a site that gets what seems to be a decent amount of traffic on the web.