I think they didn't have enough time to be discovered by a large fan base. there is a lot of other entertainment venues to compete with these days. DVDs should be released right after a season ends to grow fanbases.
when enterprise came out, my cable didn't carry UPN, so I only saw a couple of episodes my sister had sent to me on tape. then I didn't have cable when they got UPN, too busy with other stuff.
then I got on netflix and watched all the episodes. I think it was best trek spinoff. when it was coming to an end, they were allowed more freedom in plot writing and that is what made the last episodes so great. They were finally allowed to come into their own.
another series I really liked was VR5. Cancelled before the story was finished(mabye it was just a matrix created fantasy)