Malcolmshaw:
I never really thought about it, but I really don't have a good reason. Maybe it's just because I was used to playing Dungeons & Dragons. I really liked the setting of 1889, but the system really bugged me. And it seemed strange that they didn't make it compatible with Traveller.
Easiest way, if you have friends that play something particular then tell them you're going to run a Play By Post version of it and get them involved so you know what your next game should be based on.