As this is not an actual suggestion I am moving this to site feedback as it appears you want the chance changed.

Morty cards are one of the "levers" that we have, that allow us to increase the drop rate during events or when we want to push site activity.

I'll chat w/ other folks on the team about having maybe one weekend each month drop more, or something like that. I'd love to have more parts of the site be more time based like that.