Do most game jams not have a rule in place to discourage this? You would think that would be one of the first ones, but a lot of games clearly have assets right from the Unity Asset Store, as well as ones in other games submitted by the exact same users!
I'm even seeing games made months ago, submitted to every jam, in this listing.
It's very interesting seeing this for the first time, as this is my first jam. It's something I would have expected would have "died off" by now, but the practice must work if some developers are using this strategy today.