They were built to attract attention, using a combination of nostalgia and high profile brands as a draw. Las Vegas has seen many changes over the years, none as severe as casual and fine dining. Mega-resorts in all their splendor compete by using incredible themed architecture as a main draw. Literally hundreds of restaurants are inside. They're usually awarded for various reasons by Vegas publications.
Visitors associate the award with excellence.
That's not always the case. Vegas visitors also rely on food critics for opinions on the restaurants available. However, food critics today rarely mention anything bad they've experienced when dining for fear of losing an advertiser and getting in hot water with the publisher. This reminds me of a man who could have actually been the first food critic in America. He only wrote about the best eateries he knew about.