IMO, 2wd is good because:
Can compete in the EXCISTING 2WD stadium truck class.
Simple well proven design.
Fun to drive.
4WD has been tried by a couple of manufacturers, and they all sucked.
I know cause i had one of those POS' (yokomo mr4-mt), and i now have a RWD (losi xxx-t mf2) wich is way more fun.