That is because the PM in an entirely authoritarian manner took no counsel from Parliament and offered a series of proposals guided by "red lines" no one agreed to.
They voted to rule out no deal in the hope that May will prevent the law from kicking in and hoping, despite her flagrant disregard for Parliament so far, that she follows the will of the house because all she gave them was a deal that there was no view of as it was built, with no consultation that didn't work for the House.
She will not listen. She never has. She created her deal or no deal. Her leadership is the opposite of the cross party diplomacy that was needed and it has been thus for the whole of her Prime Ministership.
She has been the enemy of Parliament, a poor diplomat and pig headed leader. History will not remember her well.