Why did Disney use such crap film stock in the 1970s?

I remember growing up with Candleshoe and the original Freaky Friday, as well as The Cat from Outer Space and other such Disney movies, but only now have I learned that they were from the 1970s...

...not the 1960s as I had long thought!!

So why do these films look so old and dated before their time?

On a side note, seeing Jodie Foster as a freckly teenager like that is jarring, especially her later work like Contact and Silence of the Lambs!