Marketing is needed everywhere, pharma included. You dont spread awareness of a new drug just by filing an application to the FDA. And marketing expenses are high because potential returns are high and make or break a drug. Note that you dont have really new drugs every year so you need marketing anyway to convince prescribers why your version of the drug in the same class as your competitor is slightly better. In reality most drugs of the same class are pretty similar in efficacy and side effects, but thats a tangential topic.