Better than I could have said.
These films are of their time. Alien couldn't be made now, not the Alien we all know and love anyway. Batman '89 couldn't be made now. There are specific forces at work into how these things get made. That's why "making of" documentaries are so interesting. How they got into development, the critical reception that they received and the cultural phenomenon that they became.
Is '89 Batman as "deep" as The Dark Knight Rises? Of course not. That sort of Batman couldn't have been made. WB wouldn't allow a 2 hour and 45 minute film and there's no way audiences would want or care to see such visuals of Special Forces members being hanged or pulled out of their homes in a Batman movie. Look what happened to Batman Returns. Warner Bros. thought it was too much and went for a more "lighter, child friendly" Batman akin to the Adam West TV show, but worse. It's an evolving thing.
People just wouldn't be ready for it. There's 23 years between these films and 30 between others (Alien and Star Wars). Things change, events happen, people get older, even more cynical.
I guarantee you you couldn't have The Dark Knight Rises, Prometheus or Revenge of the Sith (not saying these films are equal in quality or related at all) with out having Batman '89, Alien and Star Wars. Can you honestly say the same thing if you change it around.
What these "classics" achieved set and laid the ground for the future. It could only have happened with that particular cast and crew that happened in those particular years. They succeeded and even went beyond what people expected them to do in that point of time. They could only have been made then.
Lightning in a bottle.