Okay, time for me to just say what I wanted to say since this thread started....
There are people who can blame "the car of tomorrow" and restrictor plates.
I'll give my take, that no one seems to want to post because "political correctness!"
A lot of the older crowd likes to "blame the millennials" for every entity that either shrinks to a shadow of it's former self or dies. Like how the older crowd blames millennials for Sears dying when it's reality Sears is dying because they suck and have a CEO who shouldn't be.... a CEO.
Well, there is a reason why NASCAR has declining ratings and viewership. NASCAR's shtick of a bunch of hillybilly's that can't enunciate a proper sentence, go around in circles 200 times then fistfight when they get into a wreck doesn't work with most millennials. As the older crowd starts to die off, you are left with a whole bunch of ever-younger people that simply aren't interested in most cases.
There is another wrinkle to this: You can also relate this what is going on to professional hockey. The NHL's viewiership declined because that league cracked down on the fights and like it or not, that is what most of hockey's fanbase tuned in to see. It seems like NASCAR seems to have a decreasing number of wrecks and like it or not, a good chunk of their fanbase tunes in to see who's going to wreck. No wrecks = just a bunch of cars going around in circles which screams "boring!" to those people.
Despite spending a fair chunk of time in the south lately, I haven't managed to develop an interest for NASCAR. I could name a few drivers, but otherwise the field seems pretty homogenous. I like the diversity of stories in drag racing - in Top Fuel there's rich and poor, guys and girls, single car teams and multi car giants, owner/drivers, tuner/drivers. Maybe this exists in NASCAR, but I don't know? But I feel like in Top Fuel a lot of people can find a background story that they can relate to. My fiance has little interest in anything automotive, but supports the drivers who were friendly to her in the pits (another fantastic aspect of our own sport that helps people relate to the drivers).
If I went to a NASCAR race, as far as I know I can't interact with the drivers and I really don't know their stories. Makes it hard to develop an interest in the sport.
Building on Samuel's point above, if I do happen to come across posts about NASCAR on Facebook, the comments from fans do my head in. It's not a community of people who seem like they're fun to be around, and if you don't have fun spectating at a race or being a part of that fan community, what's the point of being a fan?