"Noone has explained to me why we can't leave without a deal"

[Amoregentlemanlikemanner]

So, there we were yesterday in pilates and I said to my neighbour - a very gentle calm person who doesn't profer opinions very often - "they should do pilates in Parliamen to calm down". And she said (whilst working on her core)
"Noone has explained to me why we can't leave without a deal"
and after some more pilates we finished and I realised that I didn't have a succinct friendly answer. One suitable for that environment

Anyway I said as much and explained my own personal reasons for wanting to stay in the EU.

But can anyone help with something nice and short as the answer to her question?

@doireallyneedto - thanks for the explanation.
If T May had not called the election post Brexit vote, and tried to introduce the dementia tax and other crazy stuff she wouldn't have lost seats and wouldn't now be so beholden to the DUP.

Come to that if T May had reduced immigration as she promised to do when Home secretary we probably wouldn't have brexitted.

MPs are talking as if she should stay on as PM post Brexit but really I can't see why with that record. She was totally out of touch with the electorate.