[Zigurd]

It's because almost all vehicles can decelerate much faster than they can accelerate. Add to that that they may be decelerating into a corner and you can see how having a lone wheel in front is going to cause a lot more tipping over than having it in back.

[jessaustin]

The old-style three-wheelers (that they haven't been allowed to sell for decades) didn't have a differential in the back, so you had to tip them to the outside in order to turn sharply. Yes this was dangerous.

[dsfyu404ed]

You didn't have to tip them. You just needed to get them to break traction on the inside wheel. You can do that without leaving the ground though leaving the ground is a pretty guaranteed way to accomplish that goal.