Because they see it as an attempt to bypass copy protection.
Most StarForce protected games will not even RUN if you have any sort of virtual drive software loaded on your system.
I was considering getting one of the programs out there that allows you to create a virtual drive on your hard drive, specifically for running games without the cd in my case. I was curious about something, though. For maximum portability, could the program, games, and virtual drives be placed on portable hard drives? It would seem that I could then take the whole collection wherever I was going and still be able to play. Is this solution feasible? What might I be missing?