Right, but those politicians are voted in by their constituents, based on the policies they offer at the time of electioneering. If a politician is strongly in favour of a particular stance on drugs, I may or not vote for them depending on what else they are offering in terms of views.
In theory, if the system is working properly, the people in parliament should be doing what the majority of people who voted for them, want.
Our system is based on Party politics, and that was cemented in place with MMP. So, in practice, you get to vote for a package of policies, some of which you you like, and possibly some which you don't like. So the majority of people who voted for a Party may not even like that party's stance on a particular issue. Whether an individual politician is strongly in favour of a particular position is pretty much irrelevant.
I suggest that the people in parliament don't particularly know nor care what the majority want. In theory, there could be referenda on significant issues. In practice, when citzen-initiated referenda were introduced, they were made non-binding, because it's much better to get on with doing whatever they want to do than having to do what their constituents want.