The restriction is setting-specific

Battleragers are presented as a dwarven tradition in the Forgotten Realms material where the subclass originated.

The DM can change it

The published guidance explicitly leaves room for a DM to allow the tradition to exist among other peoples in another setting or campaign.

Mechanics and lore are separate questions

Removing the ancestry restriction does not automatically change Battlerager Armor, Reckless Abandon, Battlerager Charge or Spiked Retribution.

Spiked armor still matters

Even when the ancestry restriction is lifted, the subclass's main mechanics still assume access to spiked armor.