There just weren't any redheads around.
Red hair is a recessive trait and only occurs in something like 6% of the American population. So, statistically, it makes sense that, growing up, the only gingers in my life were Lestat--my tabby cat--and his successor Lestat II. (My mom was really into Anne Rice at the time.)
But, if you watched Nickelodeon in the 90s, you probably thought that not having red hair was anomalous.
The inordinate number of carrot tops on these shows leads me to believe that this particular television network was pushing a ginger agenda--pro-red hair propaganda, was the order of the day. Some might be quick to associate this apparent exaltation of the oft-maligned group with the network's orange logo, while others might chalk it up to coincidence. I, on the other hand, liken it to affirmative action--Nickelodeon deliberately promoted follicle diversity. Because of their efforts, kids like me, living in regions of the country seemingly devoid of gingers, were able to understand that "hey, sometimes people have red hair and that's okay." In those days it was about demystification, it was about integration. They were breaking the hair color barrier, and for that, Nickelodeon, I salute you(r shorts)!