Why do pro-Brexit Conservative constituencies put up with disloyal, treacherous Remainiac MPs?

I've been wondering about this ever since the referendum. For instance, a healthy majority of Anna Soubry's Broxbourne constituents - 54.6% - voted to leave, and she retained her seat at last year's general election by a mere 836 votes, or 1.6% of the total. The UKIP vote dropped by 8%, while Labour's increased by 8.1% - I've no idea whether all those voters switched directly from UKIP to Labour, but I can't for the life of me imagine why anyone who had previously voted for UKIP would be inclined to support the country's most brazenly pro-EU MP. Given that this ghastly woman seems to have spent every waking moment conniving with Britain's enemies - i.e. the unelected gauleiters of the EU - insulting Leave voters, and trying to derail the Brexit process while doing her level best to destroy her own party's already damaged credibility, I can't for the life of me imagine why her constituency association would countenance the idea of fielding her as their preferred candidate at the next election. Well, maybe they've finally had enough!

The excellent Guido Fawkes website has revealed - and published a photograph of - a letter sent by her constituency chairman asking members if they're happy or unhappy with their MP. They've even published one of the responses to it:

In case that's hard to read, the respondent has ticked the box for "Are you unhappy with your MP", and has written the following:

"Her views are profoundly unconservative. She has disparaged her constituents. Damaging the party & the country. I will not vote Conservative or campaign in Broxtowe again until she has gone."

It isn't an MP's job to take instruction from his or her constituency association on every political issue -  Members of Parliament are there to represent the interests of the whole of their constituency, the interests of their party, and the interests of the country. But there comes a point when an MP's views and their way of expressing them are so at odds with the members of their constituency association and local party members who campaigned and voted for them, that they really have no alternative but to resign as MP, or sit as as independent, or cross the floor of the house. The only circumstances in which it would be honourable to continue as a Conservative or Labour MP in these circumstances would - it strikes me - be if the local party association had been deliberately infiltrated by members of some extremist political sect, in which case, staying on might be a defensible and even noble course of action. As only the nuttiest Europhiliacs would imagine that wishing to leave the EU is an extremist view - the majority of Conservative Party members support it, after all - I simply have no idea why Anna Soubry thinks her current behaviour is morally justified.

Conservative Party members are a funny lot, and there's no guarantee the Broxtowe members won't rally to their MP's defence, no matter how badly she has behaved. But if they want her gone, I hope she has the decency to do the right thing. Fat chance, I know.