You overestimate the speed of change.
Even things we look back on now in previous decades as so obvious were done with loud kicking and screaming opposition.
Things change when those in the positions of power put themselves on the front and do the changes. Otherwise the status quo remains.
Thus we have a supposedly once left wing Prime Minister who is opposed to same-sex marriage because she doesn't want the hassle.
Progressive types in 1963 were probably thinking "Surely within 50 years from now we'll be a republic with a fitting flag". Wrong!
My Grandpa was one of those, he must be turning in his grave.
He told me not to let anyone force me to stand up for the old national anthem, or salute the flag. OK. I did get detention every monday, because I remained sitting at school assembly when they raised the flag & played god save the queen.