>>130231422Because it was kind of a doldrum for the quality of animation in the 60s-70s. Not as much money was being put into it to produce content as high quality as the theatrical shorts pre-1950s, and it was done as quickly and cheaply as possible for decades. Things only changed in the 80s when more money started getting put into animation again with all the playset-advertising cartoons resulting in better animation quality and showed there was more of a market for animation, which continued through to the 90s which became more creator-driven and experimental before winding down and becoming increasingly corporate-controlled and cost-effective over the next couple of decades until we got to the state you see today.
Not to say nothing good was produced during the 60s and 70s, but overall it was pretty bad compared to the time periods before and after it.
