Warning: Spoilers for Dragon Ball Daima Episode #2Dragon Ball Daima has already revealed that the Namekians originally came from the Demon Realm. Now, Piccolo has offered a reason as to why they left, and it fits nicely with what's known about Namekians.

In episode #2 of Daima, Goku asks Piccolo if he re anything about the Demon Realm, but of course Piccolo doesn't, as neither he nor Kami were around when the Namekians lived in the Demon Realm. He does have a little information, however, and explains to Goku that the Namekians originally left the Demon Realm because they "Don't like to be ruled." This is consistent with what Supreme Kai said about the Demon Realm earlier in the episode--that many left the Demon Realm in pursuit of freedom, in an age before travel to and from the Demon Realm was restricted.

Dragon Ball Daima's Namekians Fled for Freedom

Namekians Have Little Tolerance for Despotic Rule

The Namekians left the Demon Realm, despite having a fairly nice place to live, because they couldn't stand to be ruled over by the Demon King of the time. While it's not known who that is or what the Demon King did to drive the Namekians away, it seems they decided to set out into the universes and establish themselves on Planet Namek, as well as (eventually) having a presence on a number of other planets, such as Earth or Planet Cereal. There, the Namekians were able to rule over themselves by placing elders like Guru in charge.

This backstory for the Namekians actually lines up pretty nicely with their reaction to Frieza's tyrannical rule of Namek at the start of the Namek saga. Despite being an overall peaceful people, the Namekians maintained a warrior caste, made up of fighters like Nail, who seemed to be prepared for the emergence of just such a despot as Frieza. It always seemed strange that with as few Namekians as there were at the time, that many of them would be trained in combat, but if they always maintain a force to prevent people like Frieza from conquering them, it makes sense.

Namekians having a desire for freedom and self-determination also explains their tendency to head out to other planets and establish their own sets of dragon balls there. While it's not known why some Namekians settled on planets like Planet Cereal, it seems likely that differences in how they wanted to conduct themselves may have been the reason why. Since Namekians desire freedom, it makes sense that they would also respect that desire in others, and allow groups to split off without conflict. The dragon balls seem to exist as a last-resort option, to help them in times of danger.

The Namekians have always been portrayed as a self-reliant sort of people, even down to their unusual reproduction method requiring only one Namekian. It will be interesting to see, as Dragon Ball Daima explores the Demon Realm more, if what exactly drove the Namekians away will be revealed in the series.