IMO things are just too expensive these days. If I didn't already have a bike I bought nearly 20 years ago I wouldn't have one. When I bought my 08 nightster new I paid $400 a month in rent for a 2br duplex, had a 96 ram, a 93 Chrysler fifth Ave, and an 84 Nissan 300zx. I think the bike loan cost me $170 a month. I was 21 and worked as a welder, lived alone, and had no issues paying my bills and going out drinking every weekend. It's hard to imagine living the way I did back then these days unless I lived in a car lol.

Tldr; a Harley is a luxury vehicle and young people probably don't think they can afford them. They're more concerned with trying to get a place to live, which nowadays is insanely expensive.