Las Vegas was perfect for the Italian and Jewish-American mobs because it was a physically large but barely populated city, with great potential to become the entertainment capital of the United States, which was not the case for Cuba, Florida, etc. The State of Nevada itself was a huge area with a small population that these mobsters could easily control by offering them jobs in their dubious businesses.
Benjamin Bugsy Siegel (the great Jewish mobster) and Howard Hughes saw what Vegas could be before anyone else, which would be a haven for money and for business that they could develop by bringing in people from all over the country, especially the West, and from outside the United States. They could run legitimate profitable businesses but also cover up criminal activities.
The Italian and Jewish mobs, along with Howard Hughes and a few others, made Las Vegas what it is today, the entertainment capital of the United States, where millions of Americans and foreign tourists go every year to spend their hard-earned money, lose some money, and make some money, but also have a great time and escape their everyday tedium, which is the city you see today.