Mainly due to the functionality being dependent on other users, like some others have mentioned. None of my friends had one, so I took this thing on a bunch of family trips and never encountered signs of life from a single other user. Something about this thing reinforced the alienation I was feeling at the time (middle school) in a bad way.
I had one as well. I had enjoyed hacking on my TI-83 calculator and thought this would be a step up from that, but most of the potential seemed to be either locked away or outside of my skill range. As for using it as intended, it had the ability to communicate with other nearby Cybikos, but there was only one other person in my school that had one.