Huh, where?
For example if we're talking UK, it was banned from PE classes in 1962.
where I live, it never existed, same as most places I believe.
I didn't dig deep into the states side, but probably that wouldn't make a difference either. but There's wrestling all over the states in schools.
But definitely alot of sports are more popular than boxing in any century in human history.
Honestly, anybody who wants to support the bold claim in the OP, should have some serious statistics work to provide. TS didn't though, and nobody else either so...