It’s a perfect setup because it keeps the bike slimmer and stock cent clutches need stronger springs anyway to optimize the engagement point, but putting them on the jack shaft with a slight reduction puts them in the perfect rpm range for motor. WHIZZERs have the clutch on the jackshaft, there’s also the q-matic transmission that does it like that as well. It’s better. The clutch on motor is just something carried over from vehicles without jackshafts like go karts or minibikes.