Ad the mod said, this is specualation. Itch will generall not talk about any such reasonings in most cases.
But a quite likely explanation is, they are swamped down with other things. Things more urgent than indexing a game. Your game being not indexed does not prevent you from promoting the game. But people desperatly waiting for a payout sometimes need the money to pay rent.
Personally, I avoid games that submitted to several game jams. But that's just my opinion and I have doubts that it would affect any decision about indexing, if one was made. And I doubt that one was made. Anyway, the game page does not look like shovelware that might fail to be eglible for indexing, and there are rare cases of people that have waited for indexing longer than your account is old. If they are swamped, they are swamped.