Because the stats are based on self-identification and half of those self-identifying as Catholics also think that one can be Catholic without being Catholic.
The 50% who did not vote for Zero are Catholic. The others are bundles of contradiction who will scatter like sheep when the wolf gets close.
Reminds me of Pelosi, who is 100% for killing the unborn, while claiming to be a Catholic.
When Henry VIII made his move to dump his wife and queen and marry the Boleyn woman, even if it meant dismantling the Catholic Church and murdering Her faithful, you could say that no Catholic bishop went along with that. But you'd still have to face that every Catholic bishop went along with it except John Fisher.
Call it the "Sensus Infidelium".
Our bishops, the 'good' ones as well as the 'bad', are unanimous in their unlawful defiance as regards Canon 915. They --- and we --- are reaping the results of that infidelity.