They were ALL designed to fit adults. Never intended, from the beginning, for children or teens for that matter. That was a later thing and with (usually) a name change a la "fun kart" or "yard kart" which the latter is more a colloquial term. The first go karts were invented by speed-freak men what wanted a race car smaller, more compact and nimble than a quarter midget. You're not supposed to be "comfortable" with all the leg room of your mother's Oldsmobile station wagon. To have leg room on a kart, means it's a kart-limousine with a 30ft turning circle.
View attachment 151318
View attachment 151319
View attachment 151320
View attachment 151321
(very few kids)
Sure there's
a market for them but none produced on a mass scale. Good luck on your endeavors in that area.
Bonus points if you can identify those three grown men.