I'd say its probably not a great mystery, hobbyist motor sports are not exactly a playground for the poor. Circuit tracks purpose built for NASCAR are designed to cram asses in seats, and sell beverages with an occasional drag strip. They don't do much to let someone push their new Ferrari through a real course, or let a bunch of guys with their track toy Miatas have fun.
It's extremely difficult to get a road course track built. You have to build them in the middle of rural no where due to noise, and deal with all that legal nonsense. The few people living near there will probably hate you for it, despite it being the only real revenue source in the entire region. I can only speak for the Northeast, but I know NYST has a ton of legal issues right now, and NJMP isn't doing well financially. There's a few trying to get built in PA running into roadblocks. It usually takes someone with strong financial backing, and a community of enthusiasts willing to invest to work that magic to really make it happen. And all said and done, not that many people in the US care about racing other than NASCAR. The practicality of a circuit means everyone gets a nice view of whats happening, and a close concession stand nearby. A road course might have some metal bleachers near a popular turn and some nicer ones on a straight away.... not exciting for a casual audience, and not that profitable either.
Us two wheeled creatures, definitely bring a wider diversity of people to the track, but even then not much. You wanna see money go up in flames in seconds? Go to a track day running concurrent sessions with amaetur league races and practices. You'll see people with a few sponsors but mostly self funding show up with an 18 wheeler and full race trailers, combined with gear and bikes probably worth more than most working class homes. People who care, a lot. Might even have some teenagers looking for a break to go pro. Then you see them highside and add an extra 4-5 figures to their bill.
Point being these places are built for people with money and often in rural areas. They often require expensive memberships that encourage people to stick around and hang out even when they're not there to drive. Not surprisingly wine is also an agricultural product that attracts people with money. Just seems to go hand and hand.