That is such a good point!
Natural pearls are wild pearls-- pearls that formed without any human intervention. People used to dive for these pearls.
A pearl might be found in 1 out of 10,000 oysters. Their rarity is why they were (and still are) so valuable.
Cultured pearls, on the other hand, are farmed pearls. Technicians operate on the oyster or mussel and place a mantle tissue graft from a donor mollusk, and usually also a bead nucleus, into the oyster or mussel in order to trigger the formation of a pearl. Humans then care for the oyster until it is ready to be harvested.
Virtually all pearls sold today are cultured, farmed pearls, and this has been the case for about 100 years, since Mikimoto began selling cultured pearls. Vast numbers of pearls are cultured today. Culturing has democratized the ownership of pearls.
But the natural pearls are still rare!