No, exactly the opposite. Implementation of manifesto commitments is at the heart of modern parliamentary democracy. See, for instance, that the revising chamber can amend anything before it, and can vote down other government business but
does not frustrate or wreck manifesto commitments. The mandate derived from them is central to the formation of government.
Unhappy Leavers have been shafted by scoundrels who sought their vote based on one thing then in parliament voted directly the opposite.
If they want an MP who will not compromise on Remaining in the division lobby then they can try voting LD. They'll probably get sold out at some point as you say. There is a difference, you know, between identifying an option and wholeheartedly recommending people actually take it.