[Advice] Why do some apartments spend so long on StreetEasy?

I guess this is an advice request because I'm wondering if it's a red flag or if I should bother pursuing them.

The good apartments seem to get snatched up within days. How can these units stay on the market for so long? It seems impossible not to find a suitable tenant relatively quickly, considering how many people must be applying, so why aren't they renting? And if they're not making an effort to rent, why continue paying to list it on StreetEasy?

Edit: meant renting, not selling.