Why Mountain Bike?

I don't know what cycling is like in the rest of the world but here in the UK cycling is a nightmare.
I commute by cycle, my daily commute is 4.8 miles each way, this takes me between 15 and 25 minutes depending on the weather (I always seem to have a headwind only the intensity changes).
I regularly track my ride, and use a heart monitor to check calorie burn, this works out between 350 - 400 calories which I think is pretty good for something I have to do anyway.

So why mountain bike? in basic terms road riding sucks!
 The road I use is a country lane, a typical British B road, and Car drivers are rude and impatient, in the 5 months I have been commuting I have been clipped by several cars and had so many close calls it doesn't bear thinking about. My bike is 800mm wide with the 500 - 1000mm clearance to the gutter and trees makes me 1300 - 1800mm wide, since the road is 5m wide when a vehicle is coming towards me there is not enough room to overtake - do the maths!!!
I regularly get overtaken on blind corners, on the crest of a hill or on a roundabout, I have been overtaken whilst indicating that I am turning right, and regularly have people pull out in front of me. why?
I average 17mph with peak speeds of 30mph+ this means in most cases waiting 10 seconds would be enough to complete the move after the corner/over the hill and in the clear, in a nice safe manor.
Road riding is far more dangerous than throwing myself down a hill inches from trees at speeds of 40mph+
I am not for one moment insinuating that all car drivers are like this, I get overtaken by hundreds of cars and its just a few that ruin it for everyone, Cyclist have a bad image since like cars a select few ruin it for everyone, jumping red lights, overtaking on the inside and generally poor riding.
maybe all we need is a touch more tolerance for each other and the world would be a better place.

My next issue with road riding is, it's boring, the road is the road, the weather changes, and the gradient varies but that's it, I know that the road tomorrow will be the same as it is today and the same as it was yesterday. The trails I ride vary considerably, dry and dusty today, wet and sticky tomorrow or slippery the day after, mountain biking is a dynamic sport, a total body workout every time, and the skills constantly evolve. If you are a road cyclist I urge you to take a turn off road and see what you think. If you cycle in a gym, my advice - get a bike and hit the woods that way you get fresh air as well, or maybe cycle to the gym, that way your warm up and cardio are done by the time you get there.
I wish my commute could follow the less beaten track, it might introduce an element of fun then.

Enough moaning, I am going out for a ride.