The reason a Pikachu hasn't been released in a while is because they have been trying to fit in new concepts into the game for example break evolution and Pikachu isn't capable of ti so it was temporarily cast aside.Before Break evolution was officially announced though they did release the Pikachu and Hoopa separate boxes which came with 4 other full arts which managed to keep most fans at bay. And since later that same year Pokemon decides to release two more Pikachu EX's and they aren't even apart of the same expansion. Releasing 3 Pikachus in 3 different expansion in 1 year is something that isn't normal for pokemon so If anything it shouldn't be surprising what so ever. Also Gardevoir -EX and Mega Gardevoir -EX were already both released earlier on so giving them a tin isn't necessary and even if its the champions pokemon they aren't going to make an exception for the way they release tins now are they.To be fair though, I don't think we've had a Pikachu tin in a while (if ever?).
If anything, I would have expected to see a Gardevoir tin.