Probably because it's the most recognizable Pokemon, yet it's not entirely useful in battle, Terry.
Personally, I prefer Raichu, which I think lasts a little bit longer than Pikachu in battle, but overall, Pikachu isn't really my favorite. There's better Electric-types out there, and its stats and movepool don't really help it too much. In competitive battling, it's not even worth using without a Light Ball (from what I understand). So, I tend to get frustrated with using it (even if it means getting a Raichu out of it that may pass along Light Screen and Thunderbolt or be cute and somewhat cuddly), even though it did all right for me back in RBY.
Out of ten, I'd probably rank it at a 5. Not the worst Pokemon out there, but not really something I'd go out of my way to have.