At the Marriott world headquarters, the hotel operator has created an “Innovation Lab” to build prototype room arrangements that respond to the changing tastes and needs of customers. (Michael S. Williamson/The Washington Post)

Tourism is thriving in the nation’s capital, with the District’s visitors bureau declaring a record year for U.S. foot traffic in 2016. But at Washington’s hotels, hiring has been more or less flat for two decades.

The region’s hotel industry employs only about 5,400 more people today than it did in 1990, a tiny increase for a region the size of the Washington area. And when calculated as a percentage of the metropolitan area’s total employment base, the industry’s employment footprint here is actually getting smaller.

“We have a very vibrant, financially successful industry, but it’s just not throwing off a lot of employment,” said John Boardman, executive chairman of local hotel union Unite Here Local 25.

According to data maintained by the Bureau of Labor Statistics and analyzed by economists at the Stephen Fuller Institute at George Mason University, the hotel industry’s share of the local job market has been steadily trending downward for 17 years. In 1990, about 1.9 percent of the region’s gainfully employed worked at a hotel. Today that number is down to 1.6 percent.

Industry experts say the slowdown has been caused by shifts in the way hotels serve customers and run their businesses. The move to more limited-service options at many hotels means fewer job openings for busboys, doormen and food runners. Other job functions are being automated out as hotels rely more on apps and websites.

“There are places where you can walk into and out of a hotel without ever having to interact with a human being anymore,” said Mark White, an economist at George Mason who studies the local job market.

Despite new competition from Airbnb, hotels are not struggling financially. Hotels in the Washington region took in $4.4 billion last year, a 6.6 percent growth rate over 2015, according to industry data maintained by hospitality data and analytics firm STR.

STR estimates the industry adds a few hundred rooms every year as new hotels open in and around the city, such as a new Marriott International convention center hotel that opened in the District’s Mount Vernon Square neighborhood in 2014, or, more recently, the Trump International Hotel in the District. Each ribbon-cutting ceremony typically comes with an announcement that hundreds of jobs will be created.

So why is the industry’s labor force growing so slowly?

It could be a result of a drawdown in service in some parts of the industry. “Limited service” options such as Cambria Suites, Comfort Inn and Red Roof Inn, as classified by market research firm U.S. Hotel Appraisals, offer cheaper rooms with abbreviated service offerings. Guests who stay at such hotels will are willing to forego a full room-service menu in favor of more narrowly defined “grab-and-go” options, lessening the need for a fully staffed kitchen.

Technological change may also be contributing to the slowdown.

The hotels of the 1950s employed rooms full of switchboard operators just to enable guests to book rooms and make calls. More recently, robotic answering services mean hotels need fewer service representatives.

Tasks such as ordering room service, booking a room and even checking into the hotel are increasingly done through apps and websites rather than at the front desk.

Lackluster hiring “is a common trend we’re seeing industry-wide, and the reason for that is technology,” said Solomon Keene Jr., president and chief executive of the Hotel Association of Washington. “For services that customers would historically rely on an individual for, technology can offset that.”

Customer service is a long way away from being automated completely, but that could change as a more smartphone-obsessed generation comes of age.

The world’s biggest hotel companies are already preparing for that day: At a hotel in Tysons Corner, for example, Hilton Worldwide has been testing guest-greeting robots that could take the place of doormen.

Still, it’s unlikely that hotels will ever be run completely by robots. Automation “will probably affect the hotel industry in ways we can’t even imagine right now,” said Boardman, the hotel union director, “but hospitality is not only bricks and mortar; it’s the human interaction. It’s the feeling you get when somebody makes you feel at home.”