it’s to limit distractions, as far as I can tell. So that in an emergency they can be properly directed. (but who’s to say the emergency won’t happen mid-flight when you are using them?)
If it was about distractions they’d make you put away magazines and prohibit sleeping. The key word is “stow.” Power down and stow. This prevents your iPhone or laptop from becoming a 200mph projectile slamming into the heads of those in front of you in the event of an unexpected deceleration, which is much more likely on take off or landing than in cruise. Why don’t we have you put them away in turbulence? Well, we probably should, but people would disobey it even more than they already do on take off and landing, and being how the flight attendants are seated there’s no one to enforce it. Also, the forces experienced during turbulence are usually vertical as opposed to horizontal forces in a runway excursion so at worst it flies up and only hits you. You’re not going to sue us for hitting yourself in the head with your own laptop. Also, if you’re sitting in the front of the plane and you get a phone call or a text message sometimes I can hear interference in my headset. It’s probably not going to make the plane crash but it is annoying and lets face it, my job is annoying enough as it is.