I don't think there is a real reason for this, other Pokemon like Mismagius and Flygon hasn't had a re appearance since the DP cards either.
So not it's not only the Alakazam evolution line that hasn't re appeared lately, there are other cards as well.
It's basically just TPCi or whoever publishes the cards who are focusing on other Pokémon, maybe they are trying to publish cards with Pokes they think that people will think look cool or cute? Just a guess though.