The supposed millennial penchant for "killing" industries gets thrown around a lot, but it could really be happening to one American icon: the Harley-Davidson motorcycle.

Data suggest a considerable generational divide in attitudes toward heavyweight motorcycles, the sort of bikes sold by brands such as Harley and Polaris' Indian brand, said UBS analyst Robin Farley in a note published Friday.

It turns out that younger people do consider buying motorcycles, but for entirely different reasons than older customers, and that has potentially profound implications for companies such as Harley-Davidson, which has been struggling with declining sales and an aging demographic.

Shares of the motorcycle maker have fallen 32 percent in the last 12 months.

The survey's most significant finding is that 21- to 34-year-olds consider buying a bike for "ease of transportation," whereas older buyers purchase bikes "as a hobby" or because "motorcycles are cool."

This distinction is important, since the average Harley-Davidson customer is a married man in his early 50s, with a household income at or above $90,000. These are the customers buying motorcycles out of a passion for the product or lifestyle.

Younger buyers appear to be more motivated to consider motorcycles for practical reasons, which means it is likely they will be more interested in less expensive bikes that bring in lower margins for manufacturers.

"We believe this significant divergence in incentives to buy a new bike could be what is partly behind Harley's and broader heavyweight motorcycle industry's challenge to tap into a new segment of younger riders to drive growth," Farley said. "So unless there is a generational shift among younger riders to see motorcycling as a hobby vs. means of transportation, the outlook for the heavyweight industry could continue to be more dependent on an aging demographic."

It might not be all bad, though.

"Perhaps one hopeful sign for the industry is that younger potential buyers cited the second most common reason to buy a motorcycle is that it 'goes with their self-image,'" Farley said.

Harley-Davidson has initiated an ambitious plan to lure 2 million more riders to the brand in 10 years. Among other things, the company is setting up riding schools around the country, and it is releasing an electric motorcycle called the "Livewire." The company also previewed two electric concept bikes earlier in January.

Officials at Polaris weren't immediately available to comment. Harley-Davidson told CNBC the company has been aware of the demographic trend and it has been informing the company's strategy.

"There's nothing new here," Harley-Davidson told CNBC in a statement. "Our advanced analytic capabilities allow us to deeply understand rider migration trends. In fact, our knowledge of riders informed our strategy to build the next generation of Harley-Davidson riders globally, which we launched in early 2017."

The survey polled 2,100 adults in the U.S. over the age of 21 from Sept. 1, 2018, to Sept. 21, 2018.

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