Why doesn't the bulb for the taillight on my 2008 ford pickup work?

Why doesn't the bulb for the taillight on my 2008 ford pickup work?

Added (1). why won"t the new bulb that acts as a blinker a brake light and taillight work as a taillight when it works as a blinker and brake light on my 2008 ford pickup

It went out

It's either dead or the connection is dirty. Some fine sandpaper and WD40 will improve the connection.