Why do you need to turn off all your electronic devices before an airplane takes off and lands?
There are at least three reasons:
Reduce electromagnetic interference from any electronic devices. Less of a concern these days but a holdover from when someone might have a poorly shielded radio or tv or electric razor.
Have passengers put everything away so that nothing can become an inadvertent missile in the case of turbulence or a crash landing. Takeoffs and landings are the most dangerous time of flight and a laptop could easily fly out of your hands and seriously hurt or kill someone if it hit them in the head at speed.
Have everyone’s hands free and relatively focused. Aisles and rows also have to be cleared of luggage that was taken out. If you’ll notice, this is when they do the s afety briefing.
Now none of the measures are perfect or foolproof. Laptops have to be stowed but books are just as heavy. Sleeping passengers aren’t woken. But aircraft safety is about reducing the likelihood of an accident as much as reasonably possible and not necessarily reducing it to zero.
Electrical devices could potentially interfere with the electronics of the plane. (Find a non-digital VHF radio. Put a mobile phone next to it. Every now and then the radio reception may be degraded by a buzzing sound.) The effects of any interference would be most serious if the plane is near the ground, when the pilots have little time to react to problems.
With a properly designed and properly constructed modern device, that is almost impossible. With an improperly designed or damaged device, it becomes somewhat more likely. So the rules are there to reduce this risk.