Why do grownups listen to Def Leppard?

15ish years ago Garth Brooks came to Minneapolis. Declared they were going to sell tickets until the buying stopped. That amounted to 13 shows, at the basketball arena, capacity ~20k. Think about that. 13 consecutive days of gigs. He lived in the arena, just a simple room with a cot setup, they breathlessly showed on the news.
 
I'm reminded of this when I meet someone around my age, i.e., grew up in the 80s. In particular, when we talk music, which we do, because I ask them about it. I ask some people I meet what they've been listening to lately. Replies might be: oh whatever's on the radio, or, I don't really listen to music, or, they mention known bands, or unknown bands. All are telling.

What's most interesting, or noticeable, to me are those that declare (confess?) they still listen to Def Leppard / Boston / Journey / ACDC / Bon Jovi... or any of the big rock bands of the 70s-80s. 

Why is this interesting.

First, this single bit of info predicts their life choices in other areas (e.g., lifelong student, personal relationships, book library if any). I can accurately predict several aspects of their life choices just on this one bit of information. So can you.

Second: how lazy is it for an adult to continue to be spoon fed the same music as a teenager. Yes, I confess I had a van halen phase as an 18 year old. Yes, I went through a led zeppelin phase around then. Yes: jethro tull, the doors, the police. But I'm not in high school anymore and I can't listen to any of them now. Maybe the police a bit (best drummer in rock, yes better than bonham).  

More to the point, the world is filled with musicians making extraordinary sounds. Why would anyone want to listen to def leppard, over & over, hundreds of times? Laziness?  Nostalgia? 

I ponder what it is like for someone to never have listed to Bob Dylan's first seven records. Or what would happen if they did. Would they have the same reaction I did when I first heard Velvet Underground, Neil Young, South African compilations & Grateful Dead (all in college)? 

Acquired tastes, yes; but isn't that the whole point? Trying? When you're listening to def leppard as an adult, first of all: sweet jebus.

Second, at what point did you decide to close up your brain? 15 years old? 20? 25?