I guess some people just don't like a challenge j/k I think a lot of people just hate backtracking.
Also, I just thought about something. Since Retro was able to implement the Screw Attack and wall jumping in MP2, I wonder if we'll maybe see the Speed Booster in MP3? That'd be pretty cool to see, but they'll probably make it so we'd have to make a running motion with the Wii Controller/Nunchuck if they did.