Because May made such a mess of it the first time.I quite liked the following post I spotted under and article in The Times comments section. Appertain.
The practical madness of No Deal : Showing you are 'serious about no deal' means spending billions on preparations for disruption in the hope that the 'other side' will blink. The result is thousands of civil servants have been employed doing work that it is hoped will not be needed. Customs officers and border force officers are being recruited in the hope that they won't be needed. Ports are investing in infrastructure that the government hopes won't be needed. Business are being asked to spend collective billions complying with bureaucratic arrangements that the government hopes will be redundant. How do people get sucked into this Alice-in-Wonderland mindset?