Why do they make you close your laptop or ipad during takeoff?

You can’t even listen to music. <br><br>This has been bugging me for years. I asked the flight attendant once and she said something about interference, but that can’t be right. If that was true it would be dangerous for you to fly with a phone at all, and they even allow you to fly with a phone using GPS, but not connected to Bluetooth.<br><br>Do you think it is because of balance? Do you think everyone needs to be in seat so if there is turbulence or trouble, everyone will be in the same spot?