"Vocal" is maybe not the most accurate word for this. The reason why things don't happen despite polls showing majority support for them happening (or vice versa), is because the polls don't show how much people care one way or the other. People who care more will also do more - being vocal is one of the things, but another one is e.g. fundraising for campaigns and voting in primaries.

An unrelated example: polls show large supermajorities in favor of many gun control proposals (universal background checks poll at ~90%, for example). But most people who say that they want it, don't consider the opposite stance on that a deal-breaker for their vote - there are many other issues that are more important to them. On the other hand, the 10% that is opposed, is very firmly opposed, and that issue is close to the top for many of them, to the point of single issue voting. And when those people all turn up in the Republican primaries and vote as a bloc, those votes are enough to prevent candidates that displease that crowd from even getting to the general. And so you have all those party line votes, with every single Republican voting against, even though the majority of their constituents - and even the majority of their supporters - would prefer them to vote differently.