They have a different system of production too.
All other Gems are born from injecting Diamond sweat into a planet, draining the life out of it and leaving it hollow.
Pearls are all born from one facility on one ocean planet that isn’t depleted. Even ones older than the human race like Volleyball. >>118729360
Morganite had one, which is the Rhodonite Pearl.
Eyeball is old enough to be fully aware of Homeworld culture, predating Era 2 by an unknown amount of time, but was certain she’d be given a Pearl for her service.
Pearl implies that they are rewards for merit.
They speak with the authority of their masters but hold no rank in society. Yellow Pearl seems to be quite comfortable as Yellow’s secretary and lording it over others to Peridot in S2, Blue Pearl on the other hand acted submissive towards Steven in S5 and neutrally towards Greg in S2.
According to a flavor text for an item in one of the canon vidya only Pebbles are below Pearls in rank, but Pearls rely on Pebbles to accomplish tasks assigned to them.
Also according to the show Pearls are normally meant just as a decorative thing than a true servant, like a handbag or medal, but Crystal Gem Pearl was made more advanced: to entertain Pink and instruct her. The Diamonds just didn’t predict those two traits together would have the result it did.