Is there any reason why in-house developers would be payed less? Or be more cost efficient than an external developer.
It all depends on how the contract was built to be honest:
Does the developer receive proceeds from the sales of the title?
Does the developer receive a bonus when the software title reaches a certain threshold, either critical or commercial success?
Developing the title in-house such as Yakuza provides Sega the opportunity to recoup and control developments costs much easier, keep their developers in-house on a payroll and use them to the benefit of the company, and much more.