Did Decred developers, or did the community pay for the listing fees? I heard that Binance makes a lot of profit from it because they are very expensive.
No one paid.
CZ tweeted that it was for our strong community

They might have also accumulated some Decreds from mid-August to mid-October. Hahaha. Which they might also become responsible for the increasing ticket prices.

Will a cartel of big exchanges "becoming stakers" in the network be a failure in the system?