Some reasons for Zeerust:
A glaring example in material written before the 2000s is the lack of networked computers, email, and ubiquitous cell phones. Many authors/screenwriters bet on communications remaining difficult, expensive, and largely tied to fixed terminals. Some projects got this right better than others.
Some authors correctly predicted that helicopters (referred to as 'copters as opposed to choppers) not Flying Cars would be common place, but not as common as they expected (they have not, for instance, replaced the family automobile).
Due to the rapid, sometimes unpredictable evolution of computer technology, many an older work depicts computer hardware and software being used many years in the future when less then a decade later, they would be considered extremely dated. This is especially true in data storage hardware. A work in the 1950's might show a computer in the 2070's working on magnetic tape reels, while one in the 80's might show a computer from that same era using a floppy disk.
