So it's back to the question - these people were voted in. If they are predominantly pro-Romain then that must be what their constituents wanted
Voted in 2017 on the basis of their manifesto pledges which was to honour the result of the 2016 referendum.
MPs, as individuals, are entitled to vote like everyone else. However, if their constituencies think differently they are not permitted to ignore. Sadly that protocol is not being followed and there are still many MPs who think the referendum can be pushed aside.
As the actor, John Rhys Davis (Indiana Jones Movies), pointed out on question time the primary duty of MPs and government is to preserve democracy.