NASCAR will be hurt in the short term, but I think they are banking on a more mid-long term financial view. They know their shrinking fan base is old and dying (thankfully). They know that to build a younger fan base who grows up watching and thus become committed, they need to pivot to a younger (i.e, less racist and less white) audience. OTOH, in the short term they know they will take a hit, especially in actual in-person attendance and the kinds of fans who follow NASCAR around the country in their campers (often plastered with confed flags).
Only 30% of all NASCAR fans support the ban, including Northern and casual, TV viewing only fans. That # is even lower for older fans and Republican fans. Those who actually attend the races skew older (the oldest fanbase in sports) and Republican, and southern. So I bet less than 20% of those who actually attend races support it the ban, and somewhere between 25%-50% oppose it enough to boycott. I will also be very surprised if thousands of fans don't show up wearing confed flag shirts hidden under tshirts they take off in the middle of the race, forcing NASCAR's hand. Over time, some those racist fans will be replaced by those who now avoid the sport b/c of the racists, but I think it will always be a highly conservative leaning sport.
There's an inherent right-wing appeal to a sport about gas guzzling, polluting cars flying around in a circle, plus there's been 70 years of "southern" pride branding they drew many racists to it just to be with other racist. The GOP Southern strategy included alliances with NASCAR and appeals to their fans.
And NASCAR had long ties with racist segregationist George Wallace, allowing him to campaign there and letting his wife be the first woman to drive the pace car, and later Wallace hired the former NASCAR president to be his campaign manager for President.