Craigslist never sold afaik, theres loads of other example companies worth more than a billion now that never sold. Depends how you define "project" of course, but you gotta make sure you don't define it such that this would no longer be a "project" when it's worth 1bn. Also everything that sells for more than 1bn is something that presumably nobody would sell for 1bn.

The idea that anyone would sell any project for 1bn is kinda nonsense, if a project looks worth buying for 1bn to someone, it may look to be worth keeping to the people who made it or are in control of it.

I'd probably sell any project of mine for $1m, I'm very cheap.

That is literally their point.

Incorrect.