I see two different questions in the original post.
1. "Her question to me was, "Why do people choose a Harley cruiser type bike over a lighter weight, more manueverable bike?"" I read it with an implied "... as a beginner bike?" at the end.
2. "Can anyone else add any insight as to what makes the HD popular besides being part of the "cool guy" crowd?" Love this question, because it provides one answer already.
Anyway, some internet thoughts on these two that are worth what you pay for them.
1. I can only guess information from peers and successful marketing is the largest contributor in the first choice for new riders. New riders haven't ridden much, so they seek advice from those who have, and many of those folks tell them that they'll have the most fun on a Harley. They get pointed in that direction and the choices narrow down and new rider ends up with a Harley. Having said that, I also think many folks do like the way Harley's look, and style is a factor. It adds together. I tend to think the light weight bikes are easier to learn on myself... it's just one less thing (the heavy weight) to get in the way when you're trying to learn this new skill. Even though I ride a big, fat Road King, I have ample opportunity to ride 250 street bikes, and I enjoy the light weight very much, particularly in city type riding. I hope Suzuki sells the heck out of some TU250s. Love that bike.
2. I can only tell you my own thought process. I wanted wind protection, fuel injection, and a bigger motor on which to do day trips. Originally, I wanted a BMW RT. I still think they are about (for me) the most comfortable seating position out there, they handle just like I like, are light relative to their competitors, and have the best weather protection I've personally sampled. But, I shied away from it because I was less familiar with servicing myself the mechanical/electrical aspects of it and I didn't want to learn it. I knew that if particular things broke, I would not want to pay the dealer service fees and would not feel comfortable doing it myself, so the bike would atrophy before my eyes. I like the look of the Road King and there is a (perhaps unsubstantiated?) vibe out there that every Bubba on the planet can work on a Harley. Not to mention, they have a great reputation for reliability, and my bike is stock. They are a very well-known and supported entity. I have (surprisingly, to me) very much enjoyed having local resources to call on when I need something.
I don't ride it like I rode the SV650 or the Honda RS125 GP bike. I drive it like a 1950 Buick street rod, right at the speed limit with my arm hanging on the window. When the fast guys come up behind, I pull over. It's a nice place to watch the world go by. With the 'Stich and full face, I look like a BMW rider that stole a Road King.
Other bikes I would like: St13, RT, Honda Deauville or NT700 (whatever it's called).
Other thoughts I like:
From Davevv: "There are also a lot of us on Harleys that buy them simply because we prefer the "feel" of a Harley." I like that feel, too.
From Joexr: "HD riders just SIT on bikes going down the road a lot."
I do a lot of that. I also want to own a supersingle and do track days again someday.