Carol Danvers/Captain Marvel origins involve the Kree, so they couldn't introduce her until they and the more cosmic side of the MCU emerged.I have to wonder if the plan to do a Captain Marvel movie isn't partly motivated by DC/WB announcing a Shazam movie? I have no clue what the exact legal details would be, but maybe, as with Marvel's motivation for creating a character with that name in the comics, they feel the need to assert their copyright onscreen as well.