Distance. A 3-4 hour race on an oval ends up being 500 miles, whereas a stock car on a road course can only cover ~100 miles in that amount of time.
And in a sport where average speed over the entire race is all that matters, you want a very large sample size. Especially with all the variables like lap traffic that have to even out.
It also has a lot to do with competition. Those cars have a MUCH harder time passing one another on the road courses. More passing/lead changes typically equals more exciting racing (and more exciting crashes). An oval with 2-3 grooves allows a car to pass even if it's only .05 seconds faster per lap. A road course with 1 groove means you can hold up a guy much faster than you for days until you make a mistake. This problem is especially magnified when you have to pass each of the lapped cars 20+ times a race. The extra lanes allow for everyone to pass the lap cars evenly, whereas catching a lap car in the corner of a road course can take you SECONDS longer to pass than it does for the car behind you because he catches the lapped car on the straightaway.
This also means if the fastest car in the field starts at the back of the pack (due to a transmission change or something) he has ZERO chance of ever making it back to the front. In fact, the winners on road courses almost always start in the top 5, that's just how hard it is to make it through the pack. Meanwhile, people win from 43rd on an oval no problem.
The different grooves also make for much more varied racing and car packages. One guys sets up his car for the top while the other is dialing it in on the bottom. And then their tire wear becomes different which makes things even more interesting, along with tons of other strategy spin-offs (like I'm faster than him, but we're both running on the bottom, and if I go to the top now i'm too slow to pass him).
Probably worth mentioning the camber and banking on ovals as well, which just leads to much faster racing. Some people just flat out prefer watching cars go over 200 mph. The crashes are epic, and when you have things like 'the Big One' go down in EVERY single Talledega race, people really enjoy that. There's so much history at all these tracks, I can't see Americans giving any of them up. If you like road racing, watch tiny/light cars, and let the big high horse engines that are put up front and equipped with only 4 gears continue to go fast.
That said, I'd love more road courses in NASCAR if possible, and there should be one in the Chase since there's at least 1 of every other track type. Marcos Ambrose was always my favorite driver, RIP (and that haymaker he threw last year was sooo perfect). That final lap at Watkins Glen with him/Keselowski/Busch sliding everywhere because of the oil was absolutely the most exciting thing I've ever seen on television. I think a separate NASCAR series for stock road racing would make the most sense though (regardless if they're vettes/porches or jettas).
And this will probably be the last post in the thread because most people in Mass. (and the rest of the north) have no clue what NASCAR is.
EDIT:
https://www.youtube.com/watch?v=VFrp_HuzsvY@ 43:00