It's likely designed for safety (in a cheap way) so that the thing isn't left on and running for too long. It probably can't properly get rid of the heat it generates fast enough to run continuously. My (higher end, but still made of plastic) burr grinder insists on only running for about 30 seconds at a time because I can't afford an all metal behemoth like at the local coffee shop that can chew through several pounds of beans in one go. The machine needs time to cool between so that it doesn't wear out prematurely.
Also, for devices in homes that have the potential to chew up an entire head of hair or suck in a loose bit of clothing like a tie in an instant, it is good to have their operation tied to a dead man's switch.