Television was just getting popular, Superman was on TV, girls were focused on dolls, Barbies, and they were pushed towards Archie stuff if any comics at all. Seduction of the Innocent was fresh in the mind of the parents of Baby Boomers, so lots of parents were tossing comics, and she didn't really have the same kind of powers as Superman or Superboy...and then DC published a competing character, Supergirl, ,she could fly, had a flying horse and she had all of Superman's powers!.
Wonder Woman comics were not found as often on newstands, they didn't sell as well. Girls were watching Donna Reed and Gale Storm/Susie and wanting to grow up like them. This was way before the women's movement. Veronica, Betty and Katy Keene were more the type that the girls of that era looked up to.
I'm glad it changed;)
Thanks,
I remember I had only been collecting for a year back in 1999, and had already noticed how hard it was to find 50's WW.