For me its usually the weather, the timing (family events), and the fact that I already go to every home game.
Years ago I got turned off by the fan experiece they held at Coleman Collesium. Nothing but a fustercluck of people cutting in line to get one players autograph. If UA knew how to better organize events for fans, then I might go back. But every year ADay and now Fan Day all I hear is horror stories about long lines and dissapointment.