I own the box and CS version of the 757 and if i was to guess.. its down to the contracts at the end of the day. For me the JF757 boxed is a very stable aircraft and i never had issues other than learning how to use the FMC and do me flight plans and the boxed version is a top addon to have. I brought direct from captain sim to make sure i have the latest version quicker and to show my support to the developer by buying it direct.

The pricing between the box version and the cs versions it quite a bit different with the boxed being the cheaper.