Because it looks scary
Pumpkins are used to carve jack-o-lanterns.
we carve jack o lanterns because stingy jack tricked the devil into going to hell and the smile is to represent jack's smile when he did
Pumpkins are used to carve jack-o-lanterns.
for Halloween decorations
Turnips
Ireland used Turnips as "Jack "O" Lanterns"
pumpkins
Turnips were carved instead of pumpkins.
Actually jack-o-lanterns can be made out of any fruit or vegetable; it's just that pumpkins are large, and easy to hollow out and carve faces on.(It is believed that the first jack-o lanterns were made from turnips)
The Celtics originally used turnips as Jack-o'-lanterns. They would carve faces into these root vegetables and place a candle inside to ward off evil spirits. This tradition was later adapted in America, where pumpkins, which were more abundant and easier to carve, became the popular choice for Jack-o'-lanterns.
Pumpkins you idiot
Pumpkins, and in other places, turnips.