Because as I recall the MSFS is just a quick VC model and external model based on the default MSFS 747 systems / gauges; where the P3d version is a ground up build / coding of 767 systems and everything... But if you have the patience to wait, usually around mid to late December Captain Sim these past few years has offered an "everything for $9.99" sale (was on the 21st and 22nd respectively these past two years...) That is when I typically buy my CS stuff... I know they send out an email to let you know when they are having it..