It's not a very unique take, but the self promoters do just yells very loudly.
There is many ways of doing this, and here is just some ideas.
1) Remove all self promotion from the Community page. Especially in the first week of the jam. The same should happen to all peoples that just write 'good game' to all or nearly games.
2) Use the Community page to make a positive and constructive Community, by telling what a jam is and how you are suppose to behave when you are part of a game jam. And use the Community page to;
- Bring focus to games that need ratings and feedback.
- Tell people how they can write better feedback. Tell them that good feedback is not about self promoting, and tell them that feedback is both to tell what is good, but also bad about the games.
- Tell them that 'rating for ratings' is something we just have to do, and it's not something we need to ask for.
3) There should also be a video introducing how we should take part of the game jam. Here it's important that there should be more focus on the community part, then on the game making part. Of cause it should also have a focus on the game development.
4) I would love to see a price given to people fighting for making game jam communities better.
5) Streamers/youtubers that will focus on playing, rating and giving feedback to games that really needs it, could also help. They can also put focus on what we expect from game jammers.
6) I know when a jam starts here on Itch, it's possible to write a email around to everybody that tells things about the jam. Here you can write again what we expect you to do, when your are taking part of a game jam.
7) It's also possible to remined people, when you are given feedback, that they are expected to do the same thing. And I here don't say that you should self promote, but you should tell them to play, rate and give feedback to games that needs it.
8) When we first begin to have a better community, there is high chance that we begin to remind each other how we are suppose to behave. This is the culture I am taking about.
There could be done a lot more things, but the goal should be to make games jams better for everyone and not just for the self promoters. In the end it would create a even more active and better community, that is not just about ME but about US.
I strongly believe it would make game jams more fun for you, and it would make it more fun for everyone else. Self promotion at best helps you, but it does not help the community.