It's a lot more work to set up two Eelektriks, get two energy in the discard pile, and often use a Switch than it is to get out Mewtwo and DCE.
Usually in the early-game, they're so focused on setting up other stuff that they can't pull off the Mewtwo+DCE drop, and if they do, it leaves their field weak and open for you to come back. I used to think the same thing about using X-Ball early game, but after trying it out myself, it's not as risky of a strategy as it first appears to be. I actually ended up dropping Thundurus completely because it was so inferior to Mewtwo.
Usually in the early-game, they're so focused on setting up other stuff that they can't pull off the Mewtwo+DCE drop, and if they do, it leaves their field weak and open for you to come back. I used to think the same thing about using X-Ball early game, but after trying it out myself, it's not as risky of a strategy as it first appears to be. I actually ended up dropping Thundurus completely because it was so inferior to Mewtwo.