As far as I can see, every political party is backing this. Why?
Because they think that if they oppose it they will look nasty. Nothing more nothing less. They look across at the competition going down this route and think "mustn't be left behind, mustn't be on the wrong side of history, we'll lose votes". They couldn't give a toss about having a plan that fits together logically*. They are not thinking of the long term. The far-seeing of them are thinking as far as June 2022.
- look at the planning that was done for Brexit.