[laumars]

Because of ergonomics. When you watch something on TV and movies you want your actors to do exaggerated movements to really capture the attention of the audience. But when you operate a computer you want your movements to be as little as possible or else you quickly get RSI.

Edit:

It’s also worth adding that SciFi operating systems are not general purpose ones. They’re designed around a specific function, a function that’s typically integral to the plot.

[PaulHoule]

Like that scene in the minority report.

If you hold your arms in front of you and make big sweeping motions you will get tired and sore.

Touchscreen monitors for desktop PCs are technically practical but haven't really caught on because they are tiring to use.