Project Photofly is only at the technology preview stage. The goal is to perfect the technology of converting 2D digital photographs to 3D models through customer feedback. So all we need to do is pick a platform where the audience is large enough for us to get feedback to guide the technology's development. The number of users on the Windows platform is large enough. Should this technology ever make it as a production web service, then the Mac would be a potential client. For now, it is possible to run the Photo Scene Editor on a Mac using Parallels/Boot Camp.
Explanations are alive in the lab.