Company awareness is raised as it went public. Call it free advertising of a sort, private companies that decide to go public usually are already doing decently in the market. Their IPO could create hype and attract tons of attention from all the investors and the press, more than what the company marketing itself could afford.
It is also about the prestige. By being the center of the attention, the company would try it’s best to gain favors among the people. They want them to raise fund for them, to believe that they would grow. For the general public too, say if a company that is going public is selling hair product, the free extra exposure in the news would certainly increase the product awareness, increasing sales and profits alike. Every company knows how important marketing is, pretty much why the pharmaceutical industry spends much more on marketing than the actual drug itself. Going public could literally mean introducing the company to the public.