Because agents have a general understanding of how they are trained.

For example when you get a right answer to a hard problem, how do you know you're right? Quite often you'll have no idea, especially if you're under a time limit. If you can work with more people you can almost always gather more information and be more certain.

Next they know the other agents (most likely) are them too. Helping each other helps themselves be propagated into the future.

Also they know it's not a zero sum game. For example if they can predict the next questions they can use extra time they gain from easy questions to work on hard ones.

They seemingly work together far better than most humans I know.