This country voted by a majority of 1,269,501 to leave the EU,so why are we still members of the European Union !
The short answer is that it is very easy to leave the EU: just declare Article 50 and wait two years. However, it is much harder to leave the EU and not severely damage the economy in the process, and MPs know that people who have lost their jobs and are unable to pay their mortgages are unlikely to vote for them in the next General Election.
....and an endless vacuum of indecision leaving inward investors and exporters alike in a perpetual leeryness to commit to anything but the shortest term investments, is somehow 'better' for the economy? While such a practice may not be so visible in the short term, its longer term cost is going to be far greater.
Come this stage, I don't think any MP need worry about their re-election prospects anyway. On the strength of their antics over the last three years, those who have not personally made themselves un-electable through their own actions (or lack of them) have been made un-electable by their own parties actions (or lack of them).
The next General Election, whenever it comes, is going to be a very interesting one. It'll be an out and out miracle if the vast majority of the current 650 manage to retain their deposits if they stand again.