Funny you should mention it. I traded the only HD I ever owned for a new K75C in 1986.
My guess is that many of the HD and cruiser crowd, as has been mentioned, got into it to adopt the image. That image is well-defined in the popular media of the last sixty or seventy years and if they have little or no MC experience there is no reason they would be expected to feel otherwise. Education and observation are what brought me to wear what I consider appropriate gear when I ride.
These rider's sense of style is different from an ADV, RacerBoi, or an IronButt rider. Stereotypically their rides are short, their destinations often involve ogling each other's chrome over a brewski and the aim is to support an image that has been well-marketed for decades. Many just want to be unique, like all their buddies around them. Is this any different than the other sub-classes?
As a teen I enjoyed reading Easyrider magazine and dreamed of owning a Harley, but had to make do with a Suzuki TS100. I went through twenty bikes before finally purchasing a Harley. When I did, it was a Sportster 1000, as I had come to appreciate handling and performance and the other bikes in the HD line couldn't even try to deliver. It was the first new motorcycle I had owned, and it was a disappointment.
I tried to like it. Really I did. I tried to find joy in riding helmetless with jeans and a jean or leather jacket, boots and gloves. It was uncomfortable riding this way, having always ridden with a helmet. Putting in 400 mile days was a pain with the tiny gas tank. Wind, sun, and weather all will wear you down on long rides. Those noodles for forks were the clincher for me. I'd crank it into a turn, or try to transition between curves and have to wait for the steering input to translate through the flexy forks to the wheel. The bike had less than 10,000 miles on it when I traded for the K75C, bought a Roadcrafter suit and racked up 80,000 miles over the years before finally selling it.
In the mean time I still rode with guys on HD's who were the real deal. We were buds, but I know it was embarrassing for them when we went to, say, a Gypsy MC rally in Del Rio and amongst the pirates was me on a blue bike with a blue suit, looking all GQ. They'd always threaten to use my bike in the bike bash.
But we were all riders and that would win through once they took the time to realize I was an all right guy, even if I dressed funny.
These guys were content to ride long miles, day after day, in all kinds of weather. We had some good times and respected each other's choices.
I'm just glad that we all ride. Riders are still better than non-riders in my book. If you ask me what I think is best, I'll tell you what is best for me. As for other people, I really do try to avoid preaching gear choices. Everyone has to find their own path through life and evolution must take its course. Some who prefer pirate garb will ride into their golden years and some who gear up to the max will get dead young, despite being well prepared to avoid injury.
If someone has poor skills and poor gear choice, and, I care enough about them to intervene, I will probably point out where they might consider focusing in order to preserve themselves. Once.
The bottom line for me is that I want to respect a person's choice, offer information if it would be well received, and avoid doing things that divide riders amongst themselves. Riding can be something different for each rider and if they need to dress a certain way to get that something, then so be it. At least they are riding.