It's all trade-offs. Wax paper is inferior in some ways - wax melts at low temperatures, can affect flavor, is less durable and strong, and might be more expensive than some alternatives.
When packagers make billions of units even fractions of a cent add up to real money so the incentives to minimize costs are intense. Even if wax was superior and cheaper it might be heavier, and that alone could make alternatives a cheaper solution.
It's a complicated issue and regulation is a good approach. We should test everything in our food chain and regulate it carefully. Industry keeps putting poisonous things into our food and water because it saves money.