Things take years, sometimes decades, to be considered "classics", as
EviLore
explained earlier in the thread.
The Empire Strikes Back was trashed almost as badly in 1980 as The Last Jedi is today, but now everyone says it's the best Star Wars movie.
40 years later everyone remembers The Empire Strikes back, but no one remembers other 80s sci-fi movies like Alien Dead, Galaxina, or Death Watch. If you look more modern to something like 1998 a movie like Armageddon or The Big Lebowski can be consider a "classic" now while stuff like Phantoms or Soldier (a BLADE RUNNER spin off) are more forgotten.
Like
EviLore
says, it takes time for the shit movies to be forgotten and the better movies to be considered classics.
The elephant in the room that's missed by this is that back in the 80's genre stuff was still, by and large, dismissed by the mainstream critical establishment as being unworthy of serious regard.
If you think the reviews of Empire are sniffy, check out the reception of other genre pieces around the same time. Recognized classics like Alien got short-shift, or were straight-up panned by the critics.
Genre enthusiasm was limited to a relative handful of publications, with the initial boom of interest that followed SW box-office and cultural triumph in 1977 having diminished greatly by the time the 80's arrived. Starlog, Starburst, and to a lesser degree Fantastic Films and Cinefantastique, were the only magazines with notable circulations. It was a very small world.
Its funny, I can't really imagine people who weren't around at the time being able to fully understand how different the pop-culture landscape was back then. Genre stuff didn't become mainstream overnight, what actually happened in my opinion was that it ramped up over time in a series of waves triggered by particular IP's becoming big popular successes.
A bit of a history lesson: SF was pretty much dead for most of the early 70's; you can count the number of major productions practically using the fingers on one hand and none of them were successes really. The only significant franchise was Planet Of The Apes, and that was more action/social commentary than hard futurism. It was not an optimistic period! We're talking about dystopian visions as shown in Soylent Green, Silent Running, Zardoz... hell, the "great white hope" of the pre-SW 70's was Logan's Run.
The big kahuna of that period were disaster movies, later succeeded by the eco-horror boom kicked off by Jaws in 1975. A short lived cycle where a big-hit is followed by copyists for a few years in the same manner that The Exorcist in '73 resulted in a slew of possession-themed horror movies.
Space Opera as popularized by Star Wars was on a very similar trajectory by the end of the decade, and I'm pretty sure the critics of the time had expected it to go the same way as the previous cycles. What happened instead though was a bunch of big breakthrough hits which although thematically quite dissimilar, all fell under the broad umbrella of "genre" strengthening everything culturally in the process. We get Alien in '79/'80. Raiders and Road Warrior in '81, E.T. in '82, a concurrent resurgence in horror started by Halloween in '78, codified by Friday the 13th in 1980...
By the mid-80's everything is kinda mixing and converging into bigger cultural wave which explains stuff like Ghostbusters and Back To The Future, and we're really off to the races. What was happening was very apparent to me because I was always into this stuff, and I got to watch as it transformed from being an "outsider" area of interest into a thing for everyone.
You could see this in how the specialist shops changed radically over the period. At the start of the 80's you could go into such places and find all kinds of oddities left over from the 70's, but a few years later this was all picked clean replaced by current product and increasing amounts of merch. You could literally see it changing in front of your eyes, week-by-week.
Anyway, sorry long rant, and I've left out the simultaneous rise of video gaming and comics in the 80's which were also massive contributors to the seismic shift that occurred. Point being, the critics of the day were not good at adapting to all this, hence the disdain and often incomprehension of their appeal.
