Why did every sci-fi movie made in the 70s look like the interior of a Southern California mall?
That's because a lot of modern architecture looks futuristic. Especially if the public hasn't seen it before. For example, here is "Operation: Annihilate!" -- from the first season of Star Trek. This shot was the entrance to the cafeteria on the TRW Space and Defense Park (now the Northrop Grumman Space Technology headquarters) in Redondo Beach, California.
This shot is on the sidewalk outside the same cafeteria building on the TRW space campus.
This is UCLA. But again, "Operation: Annihilate!" used it for the surface of the planet Deneva.
Conquest of the Planet of the Apes used the newly-constructed Century City office and retail park for their "city of the future". It simply hadn't been occupied yet (by ape or man).
Marin County Civic Center in San Rafael, California, served as Ethan Hawke's office in 1997's Gattaca.
The interior of the Bradbury Building in Los Angeles was Harrison Ford's house in Blade Runner. The structure was originally built as a department store.
I can't tell you how many times I've walked on the street in front of the Ghostbusters building -- 55 Central Park West in New York City.
The Royal Palace in Caserta, Italy, was used for Star Wars: The Phantom Menace and Star Wars: Attack of the Clones. It's not modern architecture, but then Lucas' story wasn't very original, either. Nor very much about science fiction; his stories are set in the future, but really are tales about princes, damsels in distress, knights, and kings.