It seems a little exclusionary, doesn't it? The red, yellow, and orange bell peppers get to have fun together in a multi-colored three-pack while the green bell pepper is always on its own
But there's actually two good reasons you don't typically see the green bell pepper packed in with the others. It all comes down to cost and taste.
Yellow, orange, and red bell peppers are just the ripened form of their green counterpart.
Because green peppers are harvested before they're completely ripe, they require less time to produce and are thus cheaper than other colors.
Because green bell peppers are less expensive, grocery stores usually refrain from adding them to the multi-packs, as consumers have found them to be not cost-effective.
When some retailers did try to package them together, the green-yellow-red packs weren't big sellers.