[Getter Robo]

I think it's because revos and maxxes are easier to convert than lst2. Heck you don't even have to build anything yourself if you want to make an "ubermaxx" or a "G-Maxx-BL-Revo".
For the LST2 you have to do at least your own chassis plate for batteries and e-maxx tranny or a motor mount depending on how you want to do the mod.

I dunno how hard it is to convert a MGT but it doesn't seem that hard. There should be enough space for the batteries to begin with.

LST and MGT have one thing in common: You don't have to load them with hopups to make them work with crazy motors unlike maxx trucks.