MPAA Rating Change

This movie was rated GP when I was a kid (it was the forerunner of the PG rating....same meaning.) How is it that the film is now rated R? I've noticed this has happened to a number of films from back in the early 70's that used to be PG, and have been changed to R.

It's certainly not because parents are more conservative about what their kids see these days.....if anything, the exact opposite is true. Anyone know what the criteria is that the MPAA uses to snatch away an existing rating and replace it with a new one? I realize that a filmmaker will sometimes appeal an R rating to get a PG or PG-13....but never the other way around. After all, moviemakers want MORE people to see their films....not less. This leads me to believe this is somehow at the behest of the MPAA....what gives?

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