Because humans are nearly incapable of projecting in a non-linear way. As in, it takes active educated effort. Most predictions you will see are linear extrapolations of what we already know. That's why flying cars were a popular "futuristic" scenario. They can drive now, why shouldn't they be able to fly in 50 years from now? That thought was prevalent in the 60s.

How should they even know that cars will become globally connected smartphones on wheels first? Smartphones didn't exist. The microchip didn't exist yet. The Internet didnt exist yet. It is impossible to make this combination from the 1960s perspective.

Complex non-linear systems don't work in intuitive ways and minor changes in fundamental variables can chaotically change the system in entirely unexpected ways. Non-linear developments will always be surprising, it doesn't matter how many Youtube videos certain pop scientists are creating.