Down to several factors...
a) Those who were in power before the referendum who were adamant they couldn't lose because of project fear
b) The incompetence of the current bunch led by a remain supporter
c) The quality of the briefings from the pro EU civil service who dont want their shortcomings revealed by the prospect of having no one convienient to blame for their mistakes
d) The knowledge in government that they will screw the negotiations, rerun the referendum and stay
e) The EU knowing about all of this and making damned sure they dont negotiate at all.