Why are all western civilization Militaries Canada/U.S./U.K.require education for combative jobs like infantry?

[Ivory Coast Vet]

For instance in Israel,France and Dutch Army ,Spanish Foreign Legion,French Foreign Legion you don't have to take any test for physical combative jobs like mech-infantry or machin gunner ,rifleman .All you need is to pass a pt test why can't the western militaries be like that for they're infantry as well? just carious.