[Cxcvvfbgtr]

Not all of us were 9 when the original came out.
A lot of it was that prior, most SF movies were grade B atrocities (with just a few exceptions like Forbidden Planet)
TV the decade prior was Lost in Space and the original Star Trek.
With that type of experiences, Star Wars was a huge event with (at the time) great special effects.
And yes while the plot was a tad predictable, it was a tried and true one that has been used in 100s of books.
But most importantly, it was different than almost everything that had been done prior.

The prequels were all eye candy just like almost every other movie offered. It was nothing different or special.
And then top it off with JAR JAR and young Anakin to annoy everyone and you are left going "so what"