Over the last 10 years I have tracked junior drivers in the successful KRA program at NCMP and here’s what I’ve seen. Starting with a field of kid karters (say 15 entries), only a modest percentage move up to the Jr. Sportsman (cadet?) level, from there the Jr. Sportsman drivers only seem to have well less than 30-35% move up to the Jr. Class. Then the Juniors move less than half to senior classes. End result over a 10 year period you may see 10-15% of the original group of kid karters spend any time in the senior divisions.
This is because we largely follow the European karting ladder, and this is exactly how the ladder is supposed to work, as the final rung is Lewis Hamilton (only room for one driver).
Most absolutely nutso fact about karting: A 13-year-old can show up and jump into a Junior TaG kart or Jr. shifter that is fully capably of beating a senior-level kart, i.e., the junior kart is stupid fast. But that same 13-year-old can’t run an L206 because the 4-stroke classes have a 16-and-over age limit. This has been true at most of the kart tracks I’ve been to. The net result is if you are a parent on the level of the little league baseball crazies who are convinced that little Kenny is going to be a professional race driver, the opportunities abound, while if you’re a parent who just wants to have fun with a kid who is not at that talent level, the opportunities are much fewer. I have no idea why this has so consistently been the case.
It also means that karting is competing with MX for the talented kids with parents willing to allow their kids to face that kind of risk level. Net result: Not many kids.