Why Are Black Olives Canned And Why Are Green Olives Jarred?

Just a cheaper way to get them out, that's all, and I do believe that there is something in the green olives that interacts with the aluminum in the cans. You can buy different types of black olives in jars too. Hope this helps, good luck to you.

“Olives don’t come to us in edible form straight from the tree. They
have to be processed. Black and green olives (which can be the same
olives—the color is how they end up, not necessarily how they grow) are
processed differently. Green olives are for the most part intended to
be eaten raw. They are cured not cooked. Canned black olives are literally
cooked, like most anything else in a can... If you canned green olives,
it would cook them, and that’s not what you want for a cured olive
meant to be eaten raw. If you tried to cook black olives in jars (the
processing is done in the actual vessel in which the olives are sold),
you’d break a lot of jars.”

Source: Except from themorningnews.org

That is not entirely true...not all black olives are canned and not all green olives are jarred! ;)

Black olives are actually green olives cured with Lye (a poison) that become black in the process and then pasteurized. They are tasteless and not naturally cured like greek green olives.