Walking in High Heels

Recently, I was watching a cable channel that programs fashion shows almost continuously and noticed that the long-legged models prancing in high heels seem to walk peculiarly. They stride as if they are walking on a line, one foot directly in front of the other, similar to a field sobriety test. Thinking this was an odd and a seemingly unstable way to walk, I asked my wife if high heels cause a person to walk that way. She said it was just models that do it.

My question is simple. Why? It looks to me like they're liable to fall at any moment.