I’m 30 and comics were popular when I’m growing up. You’re right, only comic book nerds read them now.
I think it shows in the subject matter too. When they appealed to kids, they avoided controversial subjects because that could turn off the parents. Now, they only have a limited audience of adult collectors. So, they go for more and more controversial stories that might become seen as collectible.
Why else would any adult, probably male, buy an Archie book, unless they thought the “gay wedding” issue would be worth lots of money 30 years from now?