It's really about what ppl remember and the medium (tv) in which we watched stuff. In the 80's we got robotech(macross), transformers and voltron (lion and vehicle), these were the morning and afternoon shows, i think (it's all really hazy, i'm old). as far as saturday morning line up, i don't even believe there was a giant robo cartoon but the afternoon is where godzilla (along with other 80's staples like conan and stuff) would play, there would even be godzilla marathons for the holidays i think for like labor day?
i think it basically boiled down to what networks were able to aquire what rights to stuff, fox had saban which seemed to aquire as much giant robo as they could. I have no idea which networks played the other giant robo cartoons like robotech/voltron. (i don't think gundam was ever show in the us in the 80's early 90's, but i think wing gundam was, that's why that's popular)
then we had adult swim/cartoon network and they showed lots of anime/giant robo as much as they could get their hands on from 95 to 2003?
Things really started heating up around 94 that''s when saban bought some kind of tv rights and they made power rangers(super sentai), they kept on churning these out (i have no idea what, besides kamen rider and beetleborgs) by then i stopped watching since i was in high school, but it was on anyway since i babysat my nephews.
This is also right around the time of DBZ, at least DBZ on vhs, unless you "knew" someone (or you had a real chinatown) you didn't get to watch DBZ, which is also i think why most people refer to Evangelion as well, since it was one of the first giant robo animes to make it big, and cause a stir, right around when the internet was "getting somewhere". Then we have the internet and college, heck my anime club in 97 even held a theatrical showing of all 26 episodes.