When we compiled the limited list of Mega Pokemon that haven't been blessed with a Pokemon TCG card yet, Mega Banette stood out as one of the few with a possible explanation
The rarest or most valuable cards are, as ever, the shiny versions
This creates a two-card combo where one Pokemon can generate the Energy while Dawn moves it to a Pokemon you want attacking
Some are a rip-off and charge you just for their brand or carrying inventory when you as the consumer only care about getting that one special thing you want
Since you assume your deck is sufficiently randomized, and that you run an average of 24 Pokmon, this means you have around an 8% chance of finding one of your Claydols first than any of your other Pokmon cards
The deck is stuffed with creatures and black-intensive permanents to capitalize on Nykthos, and every permanent is able to in some way or another contribute to this