PLE actually allows you to import FBX from other software, but it only allows you to save as it's own proprietary formats (.ML and .FBL i think. .FBL allows compatibility with MotionBuilder PLE) Giving PLE full functionality would defeat the purpose of owning the business (free software does not make money), but as is, it is still a superior option for many over granting a full version for a limited time (then denying access altogether, like other software options).