alt Hacker NewsI don't understand how a blanket statement like this can apply. In a voting district where one party is heavily favored, such that that party's primary election winner is basically going to win the general election (e.g. New York City), then primary spending seems like the only place to influence the election.
The aim is not to influence the election it is to own the person who wins the election. The less likely they are to win the cheaper it is, but higher the chances it is all for nothing.