Unlike many other airports around the world, places selling SIM cards at US airports are not common. Some airport do have them, either via resellers or kiosks/vending machines, but even when they do exist they are generally relatively expensive. Doing something in advance is always a good option. (I can't speak for Vegas specifically - I'm normally in enough of a rush to get out of the airport zoo there that I've never even bothered looking to see what they have!)

Several good options have already been mentioned, but I'd also suggest looking at US Mobile. $12.50 for their "Unlimited Starter" for the first month on an eSIM and you're set. It's prepaid, so just cancel the auto-pay and/or delete your credit card using either their app or their website and you won't pay more than that.