A box is for holding, containing something, typically something non-living. Where it is a living being, it has holes for the being to breathe. So, a box is for safe-keeping, and what’s inside can’t usually come out without the holder’s (or possessor’s) help, or more appropriately, their desire or command.
Makes perfect sense why people would want to put an individual in a box. To contain them, to make them do things as per their wish, because otherwise, they are threatening. Of course, they allow some space as boxes come in different shapes and sizes, but these are eventually limited. An individual has to fit into any of these boxes. If they don’t, they will still forcefully be tried to put in the box. If they get out, refuse to stay in, they will then be put in a… cage. If the individual – as individuals go – tries to escape that, their wings will be cut. When the really determined individual (you have to know the fiercely individualistic person) still tries to break free, through the legs that remain, they will be… shot dead. And so, a box, no matter how stifling, is any day preferable to a coffin. At least, for most people.