Defense teams and events?

Why are there no incentives for defense teams to put up what is needed for an event? Right now it is all down to the kindness of people’s hearts. So an idea…

Every defense card that is event specific gets the defender ability. If they already have it, it stacks.

So for this week we need to kill purples. Under this system people are more likely to place purples, not because they are kind, but because they are stronger. This makes for tougher fights, and happier players as we can PvP our way to success. And more likelihood to actually play against something different.