I saw talk about marketing the drag racing product, which goes hand in hand with the small demographic problems, which leads into lack of sponsor interest.
I don't know the reason why NASCAR is so much more popular, but if I were a sponsor, I would drop my drag program and go to NASCAR without question because more people are exposed to my product name.
To me it seems marketing is the biggest problem, because NHRA has NASCAR beat on almost all aspects of automobile racing. More power, louder, quicker, faster, (more spectacular wrecks for those kinda fans), but NASCAR continues to have more people watching, which draws the sponsors, which draws the money, which draws the cars, which drives the action, which brings the fans etc..