All right, I'll bite. As others have pointed out, the question is highly subjective, but here are my own biases:
1. You have only mentioned "genre" movies: Star Wars, Raiders, Back to the Future. At that time (late '70s and early '80s) several transitions were under way in the industry:
1a: Jaws and Star Wars did two things - they were the first modern "blockbusters" that attracted audiences for multiple viewings of a movie, especially by young people. With a couple of notable exceptions (Gone With the Wind, The Wizard of Oz) this was not typical. Hollywood took notice. Those two movies also legitimized the horror and sci-fi fantasy genres as huge moneymakers for the general public. With few exceptions, prior examples of those genres were either cheezy as hell (insert Roger Corman movie title here) or aimed at older audiences (The Exorcist, 2001 A Space Odyssey, Planet of the Apes).
1b: Home video was about to take off. Suddenly audiences didn't have to go to theaters anymore; they could wait a few months and rent a videotape. For adults, going to the theater was a potentially spendy proposition (tickets, parking, babysitting, concessions, etc.) so that was the demographic that opted to wait for the video release (and still does). Hollywood took notice of this as well. Movies became increasingly targeted to a younger demographic.
2. Non-genre movies are as good as they've ever been, maybe better. There are just fewer of them. Pre-Jaws/Star Wars, maybe 1 in 10 movies was a pure genre picture; now 1 in 10 is a non-genre picture. You don't remember the flops. Everybody always asks, why don't they make Casablanca or The Godfather anymore? They forget that those movies were made amidst a huge output of mediocre product that everyone has forgotten about. The best pictures stand the test of time, but only time will tell which ones those are.
3. Star Wars, Raiders, and Back to the Future were made at a time when movies were still largely about storytelling, and the adult audience member was still a viable customer. Since most moviegoers today are 14 to 24 year-old boys, that's who Hollywood markets to. Movies have become a carnival ride. Movies - especially genre movies - that try to tell complex stories and deal with adult issues don't do well in the box office. Very little is allowed to get in the way of the explosions and shootouts, which look great in the trailer.
In conclusion, the final irony is that the very movies that changed the industry were the very ones that made it impossible to make movies like them anymore.