How has Piccolo Daimao been forgotten by people?

[Polyphase Avatron]

Maybe someone used the Dragonballs to wish to restore the damage and erase people's memories of it?

That someone would have definately been Kami. Although not mentioned, he probably ensured that the memory of King Piccolo would fade away, hence making mankind less fearful, and they would live their lives peacefully. Perhaps part of a Guardian's job is to make sure some things remain a secret.

And people wouldn't constantly be confusing him with the evil dictator who tried to destroy the world.

[Marco Polo]

Maybe someone used the Dragonballs to wish to restore the damage and erase people's memories of it?

That someone would have definately been Kami. Although not mentioned, he probably ensured that the memory of King Piccolo would fade away, hence making mankind less fearful, and they would live their lives peacefully. Perhaps part of a Guardian's job is to make sure some things remain a secret.

In fact weren't the Dragon Balls created after King Piccolo's first defeat? Maybe it was literally the first wish on Earth.

[Cipher]

It doesn't seem to be an incredibly well-justified plot point, but--

The early portions of the series lean a lot more heavily on the mystical and fantastic elements of Dragon World, so one could simply assume that a temporary assault from a demon king didn't seem too out of the ordinary, and by the time of the series proper was one of the many old-world elements less discussed or acknowledged by an increasingly technologically savvy society.

I've also always assumed that, as ridiculous as it is, the invent of mass communication and major technological leaps take place within that 300-year time span.

[Kuririn Fan]

Maybe someone used the Dragonballs to wish to restore the damage and erase people's memories of it?

That someone would have definately been Kami. Although not mentioned, he probably ensured that the memory of King Piccolo would fade away, hence making mankind less fearful, and they would live their lives peacefully. Perhaps part of a Guardian's job is to make sure some things remain a secret.

He's a God, not guardian.

[Polyphase Avatron]

Maybe someone used the Dragonballs to wish to restore the damage and erase people's memories of it?

That someone would have definately been Kami. Although not mentioned, he probably ensured that the memory of King Piccolo would fade away, hence making mankind less fearful, and they would live their lives peacefully. Perhaps part of a Guardian's job is to make sure some things remain a secret.

He's a God, not guardian.

Same difference really.

[Kuririn Fan]

Not really, but ok.

[Marco Polo]

Polyphase Avatron is right.

[Captain Strawberry]

Humans in general are stupid. Dragon Ball's just keeping it real.

Humans are forgetful creatures

[Sodhi]

What I think the reason is that, most of the people of that generation did not survive piccolo's wrath. Hence it is not known widely by ordinary people in the public. Maybe its like WW2 where in the 50's and 60's no one wanted to talk about holocaust as if it never even happened.