Brexit is the problem. Like it or not, in the democratic process the people voted to leave. May went to Europe several times to get the best deal possible. Some Government MP's voted against 'The Deal' hoping for better and the opposition to just defy the Government because they can for Political Mileage even though against their constituents wishes.
Face it, no PM is going to get a better deal, Europe will not give any ground.
Form a committee from the 21 + 1 MP's who crossed, see if they can do any better.