Because the Britsh are unable to prepare what is needed for the Brexit. That's logical as 95% of the British even have no clue what Brexit is all about.
There will not be a delay past July, it's either no deal and they pull the plug on business cycle or extension until July 1st for no deal preparations... I think the whole idea initially was for May to sabotage Brexit, but she couldn't pull that off and EU leaders have grown tired of far right activists in UK, they want them out... They are viewed as cancer and trying to break up the EU Look at videos from EU figures or what they say, the shift in the past week is completely different then from few months ago, they believed May could get them to another Referendum which stay would of won by a long shot, she failed... They have now accepted it, and rather move on and have UK-Norway type relationship then have this dragging on, having Tommy Robinson or Farage in EU Parliament is a nightmare for them it seems... It's a complete 360 from the initial sabotage plan May had, what's been unfolding has practically been a guarantee the UK leaves EU now, one way or another... The Eurosceptics made sure of it
The fact that shortly after the first referendum a lot of people changed their mind. The fact that most people have no clue about the existing trade agreements which is basic knowledge you need. Most even don't know what GDP is. The fact that the leavers even believe that they will save 350 million pound a week, which is complete nonsense as there are thousands or even million things that will change and have an impact on the economy. They didn't even know that the 350 million is before discount. A discount that runs in the billions. But even billions of difference are not noticed. The fact that new trade agreements will have to be made, and nobody has any realistic idea how that will go. The outcome of these trade agreements can make a difference that runs in the billions again. And most important: even experts admit they don't know what the impact really will be.
You know what the EU needs? LOANS. The UK needs to loan them money, and set unattainable interest/repayment rates. When the EU inevitably defaults on said loans, the UK will have a rightful and moral claim to all EU countries. They will all come under the crown, and be one big happy family, flying the Union Jack, with GBP as their currency. Brexit problem: solved. Heard it here first.
Based on documentaries and questions ask in the UK. Check Youtube if you want to have a laugh. All the leavers believe the UK sends literally every week 350 million pounds to the EU.