It’s one of my pet hates.
If it’s an overnight flight and passengers are trying to sleep, then fair enough.
But for a flight that operates entirely through daylight hours it’s completely unreasonable. It’s nannying. It’s a bit like being at nursery school and made to take a nap, whether you wish to or not.
As parabellum noted, it probably has more to do with CC trying to subdue passenger activity than anything else.