I race motocross and I am heavily involved with road biking for training. I figure combining offroad challenges and road biking would be a fun new hobby for me to look into. My question is after looking around at some cyclecross course photos, why isn't a mountain bike common in this type of racing. I mean I understand that the speeds are pretty high, and it seems that during the races there are sections that require you to dismount from the bike, so what are the advantages of the cyclecross bike vs a hardtail mountain bike with gearing changes? Thanks for the help!