MANofPIE said:True, but isn't there still 3D objects in there, right?
Yes, but we're talking about the genre, not how the graphics are made.
2D platformers are called this way because you see the action from the side.
3D platformers are called this way because you move in a 3D environment.
In Trials you're always going from left to right, on a sole axis.
It's a bit like fighting games and 2D, 2,5D and 3D types, where SF is 2D, games with side steps are 2,5D, and Tenkaichi is 3D.