I can not make a determination if they are against fire code or not, but being easy to move makes no difference.Except, ECVs in neutral are super easy to move.
Move to WHERE? So there is a fire, people flood into the hallway, the ECV is in their way - but it is so easy to roll. What do they do, roll it along with the crowd? Find a handy corner to tuck it into somewhere? Find an empty room somewhere and push it in there? Hardly likely, people are going to trip over it, and if it is in their way, shove it. Likely moving it into somebody else's way.