Double XP was great again

You do earn less.
I've seen a video that explains it too somewhere.
They double the exp but they don't double the keys, so if you were to play a game and earn 5 crypto keys say and gain a whole level on double exp, when there is no double exp you'll get 5 crypto keys and half a level.

This means you can earn 10 crypto keys per level without for example, rather than 5 on double exp.

EDIT: In fact, they even have double crypto key weekends which just proves my point. They don't double on double exp weekends, otherwise it would be a double crypto and exp weekend.