I ALWAYS found weird that Sportcars racing audience is that small... THO they appear to be the most "hardcore", especially on the internet. It seems to me they are all true fans. Huge races, tons of entries, different classes. Thats NOT for the casual viewer... While Motogo and F1 numbers are huge but probably half of that is from casual and extracasual fans. Nascar is weirdly big too, and they are a national championship. But thats fine. Their "national Championships" are all big (nba, nhl, mlb...).
I'd guess WRC fans are also more hardcore, cuz its not easy for a casual fan to follow 3 days of event, right? Tho I wonder how much in those numbers are just casual people searching for "incredible rally crashes" haha
Sad not to see rallycross on that list