Its bigger in the North East than you think. They do races in New Hampshire, Pocono, Watkins Glenn and they all sell out better than any other motorsports event. Those NASCAR fans are in the closet for sure.
I suspect a big part of NASCAR fans have actually made it to their local track to watch the races and once you've done that you become a different type of fan: one that actually doesn't mind that it loses allot on the televesion screen.
As anyone who has watched a race in person will tell you its a spectacle like no other in all of sports. The sound of 50 (or whatever they have) cars roaring bumper to bumper must be as loud as it is fast. Well at least that's what my first experience watching an oval race was like
I suspect that its so popular because unlike F1 and LeMans its very competitive (everyone in the race is driving fairly equal machinery) and unlike open wheel racing or Sports Cars, most of the names sound familiar. The drivers are American not a bunch of Frenchies, Latin Americans and Funny talkin' Brittis dudes. That counts for allot because in this country we identify with the individual and not a team or a constructor. NASCAR seems to be driven by the personalities and traits of the different drivers and the fans could care less who makes their car.
THe road races they've held, although still too sloooow for my taste, have been interesting. Watching those way toooo heavy cars take fast corners is very entertaining...now pass me some beef jerky.