Casey, attendance and viewership are declining.  Some of those reasons are the racing just isn't as exciting as it was years ago.  The cars are so aerodynamically dependent that on 1.5 and 2 mile tracks a car can get out to a 3-5 second lead and rarely can anybody catch them.  The teams are given pretty much the same parts to work with, so the main things the crew chief can do relating to set-up is adjust the track bar, sway bar, wedge, tire air pressure, tire camber (tilt of the tires), springs, gear ratio and a few other things.  All except gear ratio can be changed during a pit stop.

Ticket prices aren't too terribly awful, but you have to figure in what fans pay to travel to a race and, if they don't have a motorhome, lodging isn't cheap.  Why bother spending that much money to watch a watered down product?

NASCAR's founding father Jim France's son Brian was running the show for a while.  He was all worried about expanding into larger markets such as Chicago, Kansas City, LA, etc.  There were even talks of how to get a track going near NYC.  The majority of people in those areas couldn't care less about NASCAR and the tracks there do not make for exciting racing.  

Many old-school fans hate the way everything is dominated by sponsorship dollars which has caused network announcers to ignore the sport's history when talking about drivers of yore.  They say Richard Petty and Dale Earnhardt Sr were seven-time Monster Energy Cup champions instead of Winston Cup champs.  Drives me nuts.

I hope Smitty will chime in with her thoughts as well.  I need to get going.  Hope this helped a little.