The simple answer was emblazoned on flashing billboards surrounding Mayor Michael R. Bloomberg in Times Square two months ago. Record numbers of tourists have flocked to New York — more than 50 million last year, the mayor said — filling its growing list of hotels at higher and higher tariffs.

Last year, the average hotel in Manhattan charged $275 a night and filled 85 percent of its available rooms, according to data compiled by PKF Consulting USA. In other words, the typical hotel room in Manhattan brought in more than $85,000 last year, before its occupants spent an additional dollar on room service or on souvenirs in the lobby gift shop.

“They know the industry’s doing very well and has for the last two or three years,” said James Parrott, chief economist for the pro-union Fiscal Policy Institute, referring to the council’s leaders. Still, he added, the negotiation that led to the proposed deal was “not influenced by the broader currents at work in the economy that have been bearing down on both business and labor, particularly labor.”

Another factor is that health-care costs, the bugaboo of most labor negotiations, was not at issue here. Officials of the hotel union say their costs are held down because they provide care through four clinics that the union and the association jointly operate. The union’s members go to those clinics — two in Manhattan, one in Brooklyn and one in Queens — for their basic medical, dental and optical services.

By comparison, the union representing the workers who clean offices throughout the city, Local 32BJ of the Service Employees International Union, ratified a contract last month that was not as rich. The office workers, who make about $2 an hour less than hotel housekeepers now, accepted wage increases of just 5.6 percent over four years. By the last year of that contract, the office workers will be earning about $4.50 an hour less than the housekeepers, though they also receive health coverage with no out-of-pocket costs.