just some of the reasons given on this thread, other than random perverts molesting your DC, are as follows -
fire safety - being unable to access your child in the event of a fire or similar emergency - child being too young to make own escape
child wandering off/getting lost or injured coming to try and find you
kettles and other objects - trouser press, razor, medications, open window etc! that DC would not normally have in their safe bedrooms at home
them being scared when they wake up in a strange setting
them being scared by a thief coming into the room, or even a member of staff coming in with legitimate reason
them being scared eg by row in next door room, or rowdy drunks in corridor
the main point given though is just that it is selfish not to put your kids well-being above your own sense of being entitled to child free time to enjoy your evenings. If you want child free time - either don't have kids, or book them into grannys so you get a weekend alone with DH.