The ticket barriers are designed to only close if someone attempts to pass through without having already presented a valid ticket (a paper ticket, or a ‘FeliCa’ NFC equipped mobile phone, or an IC card), closing quickly and preventing you from exiting the gate.
Run through too fast and you could end getting a nasty whack in a vulnerable area as the doors swiftly shut in front of you!
This is an example of lean thinking or kaizen, a philosophy of efficient design with origins in Japan’s manufacturing industry. It’s also safer in a country prone to serious earthquakes!
Look also at how their machines handle paper tickets (although you rarely need one these days) – instead of having to pass the ticket through the right way and side around, most Japanese ticket machines take a variety of ticket sizes, upside down, back to front, at an angle, and are still able to read them and spit them out exactly the right way up. Very cool!