In general, sprites do take not only time but also creative energy to make, and they can't just pop up from people simply wanting them. I would gander that a lot of spriters here were possibly either busy or uninterested in making gen 5 sprites to contribute to the tcm at the time (I know I was too busy with school).
I could make a Tepig cosplay for the TCM but I can't guarantee that it'll be accepted for it. Same goes for any other sprites to be made not already in the generator.