The technodrome was vulnerable when it was stuck
 

With it stuck on that asteroid, Drakus would have no problems destroying it. Drakus didn't know where the Techodrome was and didn't show up until later in the series.

Thanks

10characters

Were you the one that said the turtles were supposed to go back in time to meet their season 4 counterparts and destroy the Technodrome? Someone said that years ago and I don't remember who it was.

I think Krang banished him from Dimension X and he never had access to Dimension X since then. I think he thought the technodrome was on earth during the entire series. I remember when Krang told him it was in Dimension X, Bizarrco assumed he was lying (even though we all knew it was in Dimension X during that time).

Why is the technodrome in 2D when it's in dimension X when we know it's in 3D, since the 87 show and 2012 share the same dimension x.

I think it's just the their typical effect of trying to disguise 2D assets as 3D models, the show does that a lot with Tang Shen's kitchen being one of the most obvious examples. That shot of the Technodrome was probably just a really crappy version of the effect, you weren't really meant to notice (although I'd say the show never managed to pull it off in any of the shots where the effect was used).

Just different animation techniques. What's more weird is that Nickelodeon Dimension X was nothing like Fred Wolf Dimension X (even if I know they were referred to as different parts of Dimension X).