Casinos don't want people to have guns (excluding their security staff). This means that even if you are citizen who has gotten better tactical training than most police and shoot more often than they do and have a CCW, they don't care.
The first reason is liability. If they ban all the guns, then in some sense I don't fully understand they are less liable should something happen. So so they think. I haven't been able to find any good case law or really anything that explains this. The closest I've come is that some insurance carriers get weak kneed over the idea and don't want guns carried around at the places they insure.
Second the people in charge don't want you carrying. This could be normality bias from "your don't need a gun here" to outright hostility and leftist anti-gun thinking. Who knows. Some of it is rich people thinking "little people" who are dumb enough to lose money in the casino shouldn't have guns to begin with.
Finally, and what I think the real answer is, some near-superstitious idea that if you ban guns, through security, signs, or magic detectors your gun problems will go away. In one sense, this is true. Credible security measures will scare off the criminal who doesn't want to get caught illegally packing. Some law-abiding citizens won't want to bother with the hassle of unassing their gun or being treated like a terrorist by security.
As far as management, they banned the guns, so after that whatever happens is kinda like an act of god. Magical thinking I'm supposing here. They don't care what happens to you; your safety is not their priority. Their priority is making sure bad stuff doesn't happen on their property to create bad PR or shutdown gambling and loses them money.
An idea solution would be, should an armed person come across the proverbial or actual radar, is to see if that person has a CCW. If they do, no harm no foul. Maybe ask them to disarm while drinking or on the casino floor. But no, that would be too hard for casinos to do.
Let's be honest. The people causing problems with guns Downtown and on The Strip shouldn't have guns at all. They probably don't have CCWs and aren't openly carrying. They're drug addicts, drug dealers, felons, and gang members. No law will stop them from doing stupid, violent, and illegal stuff.
Disarming customers and engaging in security theater doesn't make anyone safe. Private security measures don't extend to the street where customers frequently travel. So to answer the question: "Why do you need a gun in a casino?" the answer is that crimes do happen inside them, in their parking lots, and on the streets and areas immediately outside them. If I choose to patronize these businesses, I shouldn't be disarmed because of a poorly thought out kneejerk policy.
And so what if the casino is now a sterile environment? Excluding the Mandalay Bay shooting, practically all the major gun battles on The Strip happened outside of casinos anyway.
Clayton E. Cramer
Gun Free Zone
The War on Guns
The View From Out West