Sure, but in addition to everything they learn at school (and get tired of), do they really need 3x2 hours of violin, 3x2 hours of tennis and 3x2 hours of spanish weekly? + weekend tennis matches. (my coworkers kid taken as example, 12yo)
I like my job too, i learn a lot of it, but that's basically half-time of a second job (if you include commute) for a 12yo kid... that's just too much, both for the kids and their parents.
Kids oftentimes want to do that.
And with foreign languages, notably english, relying on school means they likely wont learn it.