It may be the last thing they want. It might also be something they need.
A reminder that if a negotiated exit isn't achieved we have said (by issuing article 50) that we are leaving.

It might stir the Conservative Party to get its act together. It might also remind the EU of the basic facts, the 2 year extension, and the separation payment are reliant on us getting a negotiated settlement acceptable to both parties.

It is slowly getting to the stage where "No deal is better than a bad deal" might be replaced with "No deal is better than most of the deals which have so far been offered".

It might also be that both parties are working on the basis that agreeing everything too early makes them look too eager, and if they can get agreement early on in the negotiations they have been too soft in their requirements.
It should have been clear early on that once you set a completion date for negotiations, negotiations are likely to take that time. A version of Parkinson's law may apply.