I am, unfortunately, classified as a "millennial" since I was born in 1982 and the cutoff is 80-81. What happened to Generation Y? Anyway, I think I am the perfect example of Harley's lost millennial market. Here are the issues:
#1 - My wife will leave me if I buy a motorcycle. Her favorite TV show is Sons of Anarchy and stares at bikes on the highway, but God forbid HER husband bite it on a motorcycle. There is a definite double standard there, but my mom was the same way with my dad. Our society has less of a taste for potential injury than it used to.
#2 - Harley's are super expensive. I can think of at least 5 bikes that I could buy and get more for less. I know Harley guys are will balk and say "it isn't a HARLEY". That doesn't matter to a lot of young people with limited resources. I have kids, a car payment and a wife who likes to shop. There is no chance I could justify a Harley.
#3 - Reliability: Almost ever bike manufacturer is more reliable that a Harley. The brand is not mechanically innovative and relies on arcane technology for their bikes. For a long time they could do that because people would buy them no matter what. But today people want to go further than 30-50k miles before a complete v-twin teardown.
#4 - Image: Why did people stop buying minivans? They didn't want to be their parents. Unfortunately, now half of Harley owners are 50+ year old dudes. These are the guys who will wear $5k in leathers riding on the weekend and a Hawaiian shirt with khakis the rest of the week. They enjoy chasing their Peter Fonda dreams, but it seems square and disingenuous to young people.
For me, I would buy a Triumph in a heartbeat if my wife would let me. Or any other brand. If I had money burning a hole in my pocket I would buy a BMW for its sheer engineering perfection, but not a Harley. I think most people my same age feel the same way.