Plague of Rats should give rewards for assists
Whoever gets the killing hit on the rat gets rewards for that rat, assists don't give rewards. Intentional? It's a bit anti-cooperation, why would you have others come and do the event with you if that means less rewards? There's not that many rats too, for the population now.
With decent gear they're pretty easy to 1-shot too (and not share rewards) but that's a little out of scope maybe