Having lived in Las Vegas and traveled the streets that make up the circuit...that's just how the roads are. It's not a purpose built racing circuit but poorly maintained public road coated in the mildew of sin, booze, and unspeakable vice. I can assure you that if it were faithfully laser scanned, it'd be even worse.
As for braking boards--I'd urge you not to rely on the presence of brake markers as I would advise not to become dependent on the racing line. It's the Las Vegas Strip--there are countless things around you that you can use as a brake reference. You don't use the brake markers to take the hairpin at Monaco, do you? Of course not, because there aren't any--you use the jutting curb and Aramco sign to brake and the painted blue rectangle on the road surface to determine turn-in. Absent of brake markers, make your own; it's part of the fun.