I am really curious.
The big advantage of freemium is lower friction. The people who buy your product don't typically need it advertised or explained to them. They've either already got experience with it due to being free users or they will set aside some time to trial you product for free for a while. Beyond that a free product can build up a strong reputation that carries over to the paid versions.
Billions upon billions of dollars are spent every year by companies trying to create familiarity and trust in their brands. Being able to do that with a free version of your actual product is just as worthy of the expense and in many ways a far more honest form of advertising.