The reason why we choose the TT-01 is Some of them come out as XB Pro Versions which are RTR..
Some poeple are on a Tight Budget so the TT-01 can be slided out of the box and can be upgraded down the path in the future..
So it gets them driving sooner..
The TT-01 D is still a Great Chassis and Yes does come with the Hop Ups you need but requires assembly and Time to build.. Some just want to dive in and hop up later, hence the reason for the TT-01 XB Pro..

People also tend to forget they will need Radio gear aswell and dont factor this into the cost..