It is really no surprising as the gambling cities of Macau in China and Las Vegas in America are in these countries and there is really an active gambling industry there.
But you still cant compare Las Vegas with Macau because operating an online casino in Macau is still illegal the last time i checked.
I think both Las Vegas and Macau have a big fan of gambling, but we don't know for sure how big the fan. Both Las Vegas and Macau makes a lot of money from gambling, and that makes two places will be a heaven for the gamblers. But still, there is no valid info or data that will show the biggest places that gamble the most because the data or info will always change. Maybe in the next year, that list can change as the government gives the casino a chance to reopen their business.
The two mentioned cities were a big fan of gambling and their government make a huge money through gambling but judging by the daily activities, expense and world acknowledgment, Las Vegas is the number one fan of gambling in the world and this is the reason why it was giving diverse of nicknames like Sin City, The Marriage Capital of the World, The City of Lights, The City of Second Chances, The Gambling Capital of the World etc. However, Macau makes most of its own money through the issuing of a gambling license.