....Or, because there's not enough subcategories of cycling already.
Imagine a road bike. Be it carbon, aluminium or even oldschool steel, we all know what one looks like.
Now imagine beefing up the frame somewhat, slackening the head angle, lowering the gearing and generally making it resemble something like a rigid mountain bike with 700c wheels.
Now add space for wider knobbly tyres, lots of mud clearance and maybe rack/mudguard eyes if not already present.
To what category does this bike belong if it is not cyclocross?