To be fair they’re there to represent our best interests, not just be the community delegate who’s there to just speak on behalf of the community’s wishes... but there’s an element of goodwill that if you and I vote for an MP because we like his/her party’s manifesto, then really (s)he’d be best served to vote for the policies of said manifesto, when they enter the house.
As an example if I was elected as the MP for a leave voting area that’s largest employer, by a distance, was threatening to pull out of the UK, in the event of no deal, I’d tell them, in a public Q&A session, why I’ll be voting against no deal and have it out with them.
Obviously that’s not always possible and some MP’s have received threats so if not, then they should vote for what they believe gives their constituents the best chance to a good life, even if the constituents don’t agree.
They will then change their mind on it or vote the MP out next time.
The vast majority of MP’s have voted for at least one form of Brexit and therefore most have been willing to enact the referendum result. There just needed to be more clarity on our future relationship with Europe earlier or failing that, some patience from everyone.