They're probably approaching it from a hygeine and impact-safety prospective. Two rather reasonable concerns regarding barefoot lifting:
In the same way you wouldn't walk barefoot around in a locker room so as to avoid foot fungus, now that problem is extending to the deadlift platform and squat rack (and wherever else you're barefoot lifting).
Sure, you can wear socks, but that doesn't really stop people from getting foot infections. Lots of socks have holes, and if your socks pick up some fungus then you put your shoes back on and wear them for a few hours, you've got a nice Petri dish going on. Additionally, plenty of folks are wearing rather slippery synthetic socks.
You can stub your toes. Lots of people get woozy from heavy lifts and I've banged my (Converse covered) toes into hard metal objects plenty of times.
From a lifting prospective there are lots of advantages to lifting barefoot, in socks, or even in ballet slippers. It's a rock solid foundation, and for things like the deadlift it can shave a small fraction off of the lift itself which matters when you're talking about 1RM and record setting.
Maybe consider picking up some Converse or another flat shoe that doesn't compress. A set of low top Chuck Taylors will set you back $30 (USD) and lasts for years if you just use them for weight lifting.