1. Optimistic Bias. If poorly understood new or projected technology will let you tell the story you want to if it works really, really well, it's tremendously tempting to write using that assumption. Look at Jules Verne with electricity or Heinlein and nuclear thermal rockets. They both assumed the technology would work vastly better than it actually does.
2. Dystopian Bias. In Mad Max 2: The Road Warrior the hero takes part in thrilling high speed car chases and is threatened by colorfully dressed crossbow wielding marauders. In Mad Max at Burning Man the hero is threatened by chapped lips and sunburn. Which movie is easier to pitch? And yet the second one is the future we got.
3. Lazy Analogy. Tanks will be like ships with treads. Rockets will be like ships with tailfins. Robots will be like metal people. Spaceships will be like airplanes. Thinking through all the ways the analogy is imperfect is hard work.
4. The Unknown Unknowns. Integrated circuits and the Internet have dated a lot of SF written before their appearance.
5. Futurism Is Hard. Even if you know about television, you may fail to predict its impact on politics or live theater.
6. They're Not Even Trying. Frequently the author isn't trying to predict the future: they're trying to entertain with a ripping yarn, or comment on the present by dialing it to eleven, or tell an illuminating parable about the human condition. Some of the best SF falls into these categories. As Le Guin says: "I tell lies for a living."