It's more complex than this, as there many supply and demand interactions relevant when creating a piece of software. The company selling the product knows what price it can ask for the product in a supply and demand market. This price dictates what costs are acceptable when producing the product, and this also has impact on how much they can offer the developers.

They may be able to hire more devs if they increase salary, but this would mean that the price of the end product would become too high, and they would go out of business.