Dig Dug is a screwed-up game.
Look at other games from the same general era, and you'll see the difference:
SPACE INVADERS
Aliens have arrived from outer space and they're REALLY UNFRIENDLY. Fortunately they're also REALLY DUMB. Defend the Earth!
BURGER TIME
You play a guy making burgers by walking all over them. You're just trying to do your job but the food keeps hassling you, man!