I'm assuming it is the same process as being a Featured Game. That is, it is manually curated by curators.

But what do they take into account? I'm assuming how "interesting" it is; How many participants there are. What else? Do they take into account how old it is? How close is it to starting?

But more interestingly, what can hurt its chances of being featured?

itch.io/support

Itch features jams that were made by people who are popular in some community

So is every other criteria redundant? Just popular in a community?