Appeal to Star Wars
Guten Tag Herr (oder Frau) Meier
Here is my answer to your bewilderment:
1. Remember that most the commenters saw the first 3 Star Wars movies in their preprubescent - pubescent years.
2. The storyline features clear distinctions between goodies and baddies. This greatly appeals to children.
3. There hadn't been too many cowboy movies (if any) in space before. Being first is good. Star Trek had been around 10 years before but on TV. Star Trek is also beloved by this generation.
4. There are cool weapons. The protagonists have evener cooler ones. Many boys in their forties can still clearly remember the swoosh sound made by the lightsaber.
5. There were impressive (for the day) special effects. Who cares if there is no noise in space (with the exception of Strauss)? Big spaceships and bigger explosions greatly impressed at the time.
6. Harrison Ford  and Darth Vader were breakout characters. The latter the best embodiment of badass we had witnessed. His quotes are still used to this day. The former is charismatic and went on to great things in the Indiana Jones' movies.
7. The storyline is relatively simple and linear with hints that there is more to know.
I suspect that if I had seen Star Wars as an adult, I might have thought of it as a cute childrens' film. In retrospect, my teenage self began to find The Return of the Jedi a bit too predictable.
 a.k.a The Carpenter to the Stars