Unlike traditional commercials, Public Service Advertisements (PSA) are primarily designed to inform and educate rather than sell a product or service. They have been around for decades, with the first ones being shown before the second World War.
During the war, many PSA awere issued, often citing the need to be vigilant, and support the war effort in every way possible. "Loose lips sink ships" is the kind of message PSAs would air. Over the years, PSAs evolved to cover a vast array of public interests, and are still around to this day.
The goal of a PSA is not to make a big sale, but rather to change public opinion and raise awareness for a problem. The strategy here is to educate first, and provoke a feeling and reaction after that. However, sometimes money is solicited, although usually not for profit.