Upvote:1
It sounds like a somewhat inflexible application of rules.
However, a plausible justification would be they want you to be awake and alert during the critical phases of flight. Both take-off and landing are situations where you might need to evacuate on short notice. This means it would be unsafe for passengers to be asleep, so use of sleeping aids such as neck pillows should not be allowed then. Even if you are completely awake and just using the pillow for comfort, it would still impede your ability to look around and be aware of your surroundings during an evacuation unless you spend valuable time removing it first.
Since you can't be using the pillow, it should be put away together with the rest of your hand luggage.