Originally Posted by penguinsix:
Even if you fall and die your corpse is still going to block the stroller from rolling down and crashing at the bottom. The other problem going forward is that only two wheels are touching and you have to stoop down to hold the stroller steady. You are usually two steps behind and thus higher such that keeping the stroller level means you are hunched over riding down pushing on the handles. Should there be a quick stop your center of gravity is all whacked and it's quite easy to let them go.
Think of the converse--going up. That is quite easy to go forward but going backwards up would be a bit complicated.
Of course the best thing is to take an elevator but there is usually a long line of people for that.