Yikes, liability is king here. @theat70 is right about the echoes, but now it's just the sound of dripping water (and maybe rats). I mean, think about all the broken tiles and loose railings. One wrong step and you're in a world of hurt, and the owners don't want that lawsuit. It's cheaper to fence it off than fix it up (which is kinda sad). So yeah, they seal it tight and hope everyone stays out.
Totally feel that echo comment. I've ducked into a few closed malls, and first thing you do is scan for cracked tiles near old fountains. Those spots are always weak from water damage. Bring solid shoes because broken glass is everywhere by the empty stores. If a railing wobbles even a little, don't lean on it. Heard about a guy who fell through a fake ceiling panel trying to get a cool pic.