Subsequent costs after the first game should go down. The first new gen platform game needs an entire engine and getting to grips with the platform. Things learnt will streamline efficiencies and require more in the way of 'fixing' than 'building'. The start of a console is viewed as an expensive, difficult period with a lot of investment.I think from a developer's POV they are trying to make enough money to fund their next, likely even more expensive.