I think it was 8 out of 10 at the last offroad worlds ran brushed in 2WD mod, the only brushless runners were the Novak guys.
It's probably not so bad with the new Novak Light motors but generally brushless have too much torque down low for 2WD, especially on a low grip surface, brushed have a much softer low end which equals more traction and less wheelspin.