Senator, there was a little thing called the Sexual Revolution.
Before Spielberg in ET, nobody know how to write children in a way that wasn't Disney sickening saccharine. Disney movies during the 70's were hack junk with predictable plots, lousy slapstick heavy scripts, and fourth rate actors. Disney was where careers went to die. Nobody during the 70's who was the least bit cool would touch anything Disney with a ten foot pole.
Spielberg showed Disney how to write children for a new age. For a new audience. Then in the 80's it could start to recover.
I believe it was released in 1975. Walt knew children and overall family taste very well.
Movies made by the Disney Studios after 1973 were heavy in those things as you say, resulting in the drop in revenues. I labeled them "bombs" as I was referring to the departure from the family type. There was a big drip in earning, all of which helped to bring out the today's Disney troubles.
You're right!
Did you see "It's a Wonderful Life" with James Stewart and Donna Reed last night? Now here is a classic made in 1948.