Because many opinions that serve the interests of the wealthy at the expense of everyone else are pretty unpopular unless the wealthy invest money into spreading them or distracting from valid criticism.

You're way overestimating the importance of public opinion in the US. A significant portion of Americans don't vote and those that vote and donate $ to campaigns skew older and wealthier. Who doesn't vote or donate $ to campaigns? Younger people and poorer people, who tend to vote progressive.

So you only have to focus on the politically active segment of your popular. On top of that, in many states the districts are so gerrymandered that if you're a Democrat is a blue district/state or a Republican in a red district/state you only have to win the primary and not screw up and you've probably won (or even screw up like Moore and still maybe win).

Finally, even most people who vote are not that politically astute or aware. They don't follow specific votes unless you hit a third rail issue (Republican voting anti-gun or pro-abortion for example).

Most primaries come down to personality (and a dash of political positions) and most general elections come down to the demographics of the area and the turnout.

At the end of the day, there's no need to shill for cutting taxes for the wealthy because those who vote are fund elections are generally in favor of it and those who aren't mostly don't vote in areas that matter.