Why bulb not glows when circuit shorts?

There is a concept that one must understand when working with electricity; "electrical current will always take the path of least resistance."

Many people don't understand the difference between a "short" circuit and an "open" circuit.

An open circuit is when there is effectively no return path from the electrical source back. It's like when a light switch is turned off and the light isn't on.

A SHORT circuit would be when the light switch is turned on but another wire is across the same wire pair, resulting in an effectively shorter path between the conductors of the power source. The electrical current then takes the path of least resistance, leaving no electrical current for the bulb.

Naturally, there is that gray area between a short circuit and an open circuit, that's where things run properly... in general.