I'm going to take a different tack on this than other responses: evil is winning because good is dumb.
A lot of progressive groups within the past few decades, whether it be Occupy, Black Lives Matter, or others, can't seem to actually get their policies enacted on a mass scale. In cases where politicians actually go through with their policies, those progressive groups won't support those politicians from getting voted out and having the reforms reversed.
Trump got elected, in part, because progressives didn't want to vote for Genocide Joe and Copmala. Yet, you don't see progressives building the kinds of political groups needed to wil elections like the right has.
So money can hire people who know how to argue and advertise better? That sounds like a skill issue.
And money only "buys" legislation because it is used for advertising. During its height, the NRA didn't have to contribute the kind of money that other lobbying organizations did. Why? The NRA had a large membership of people that voted.