It's the equivalent of how there was a trend to make men into bumbling idiots around Hollywood in so many sitcoms. In this case it's make the adults the bumbling idiots.

They are acting the way they do, because that's precisely what the director wants them to do. The show is cheesy by design. It's a cartoon. The cheesy dialogue and overacting are part of the shtick. And the writers and director really ask Zabka to make a fool of himself...which he willingly does.

We can agree to disagree on who is worst. Let's just say I think Zabka is a lot more self-aware that he is a caricature than Macchio is.