Is there any unconventional way to reduce CPI for mobile apps?

As the founder of a gaming company, I have noticed that although our game is popular with thousands of players in the USA, our target audience, we have been unable to generate revenue. This is because the cost of acquiring new users is high, and our marketing campaigns have been yielding negative return on investment. While I could attribute this problem to companies like Google and Facebook, I am wondering if there is a way to reduce the cost of acquiring users.