[True Republican Patriot]

Then, pray tell, why do you do such a stupid thing?

[trumandogz]

First of all, after climbing such a hill on a bike you want the reward of the down hill and second, it is fun.

[Rebelbase]

My guess would be speed, balance and adrenaline.

[HangnJudge]

Then, pray tell, why do you do such a stupid thing?

Adrenaline addiction takes on many forms
Often high risk behavior

Jumping out of perfectly good airplanes
Rock climbing
Motorcyclists (me)

All of these involve unnecessarily high mortality risk activities.
I resemble that remark...