Gary K mentioned "tranches" a nice word, earlier. I agree, there are many layers.
However: the "problem" if we want to call it one is that the average age of motorcycle owners increases fueled by the baby boomers years and we don't see as many new bikers coming on board. There are so many more 'distractions' and owning stuff even is not of interest to many millennials today, they value their time, travel and other things.
Compound this with a substantially reduced middle layer of income earners and the high cost of affordability is a major hurdle for what is essentially a leisure item.
SENTENCE IN BOLD: You nailed it there!
Finally, someone has gotten to the REAL root of the issue, not just with Harley but all the companies. It's not "other" things that are capturing the interests of younger folks as much as the actual available funds for motorcycles. It's nothing more than that, as Paul has stated.
WE are older and have had time to accumulate "things" and funds. And we (boomers) had jobs that allowed us to do that at an earlier age than younger folks today. So we started riding at an early age.
There used to be a MUCH larger middle class. The offshoring of jobs and manufacturing has had a terrible effect on what was a bigger middle class, one that doesn't exist today in the numbers we saw.
Also, the decline of unions has reduced the middle class, because those union jobs paid very well for folks that didn't choose to go to college. Many of those union jobs paid wages that college graduates wouldn't surpass until late into their careers. Those jobs allowed folks to buy and pay off home loans by the time they were in their late 40's and mid 50's. And without a mortgage anymore, we had a LOT of extra income laying around to spend on "toys".
THAT scenario doesn't exist for young graduates of high school today. It doesn't exist even for "most" college graduates either. It will take them 20 more years to get to where we were at age 40. They just flat out have more debt and lower wages, comparatively.
So it isn't younger folks not "wanting" Harley. It's that younger folks don't even have enough money to "look" at a motorcycle, be it Harley, Honda, BMW, etc. Plus, I think the ones that can scrape together a few dollars...well, they look at smaller, less costly Adventure bikes that they can go camping with and ride around on trails. Maybe this is why Harley is looking at the ADV market and Streetfighter types.