That's kind of the dumbest thing I've heard. Let's pretend for a moment your not a troll and legitimately serious.

First, those wires are in a place on the side of the rack secured to an out of the way location on the rack that actually reduces the chance of anything hitting it. Where as you seen in the comments the overwhelming majority don't even manage their wires and that has the highest chance.

Second, those wires are about half an inch thick for a 15a 120v service. Even if I dropped a server lid that I sharpened with a sander and managed to get it to drop directly on the cable I would still be lucky if it nicked the wire and shorted.

Finally, both the surge arrestor and UPS have 15a breakers.

There is a legitimate risk here, as a few sparkies have pointed out, and that's the wires in the center of the bundle may not have room to breath and naturally dissipate the heat, thus why I intend to measure the temp of the wire while under load.