I don't thing its the riders who don't like plenty of dirt,it's the bikes imho.In the good old days (80's) the bikes put out about 60bhp at maybe 11,000 rpm.Now they are around 74 and rev to about 13,500 rpm.Which is huge revs for a 500cc single 4 stroke engine.
The higher peak power the engines put out at higher revs the more the power dies off when the hit a lot of dirt,which launches them towards the fence.Thing is everyone looks for power.If they did say a 600 cc but limited the power to 70bhp at around 11,000rpm I think they would power through the dirt instead of loosing revs,gripping to hard and straightening up.Just my humble opinion.