...because it means the mechanism can be more ‘interesting’ – this is a medium size traditional Japanese puzzle box that uses two sets of ‘keys’ that slide in and out to release the end panels to move in a particular order (38 of them in this case) until the top is able to slide open... there are plenty of variations on the theme, some requiring fewer moves, some requiring more, some requiring ‘unusual’ things along the way – several designed to trap the unwary puzzler who thinks he’s seen it all before (keep an eye out for a post on the Karakuri small boxes – those are an excellent lesson in misdirection and catching the unwitting puzzler totally off-guard!).
[Note to the reader: for ‘he’ feel free to read ‘she’ or ‘it’, as is your wont. I’m very seldom accused of being politically correct. If that is going to offend, then may I suggest a better use of your time than reading my silly little blog?]