The game is destructive, of course, and juvenile as all hell, but there's no specific law against it [1], and it's not serious enough to warrant any heavy-duty police action, so the punk kids who play it tend to get away with it, especially out in the suburbs at night.
But it wouldn't bother me one tiny bit to hear that, on one of those dark and moonless nights, some homeowners were to catch up with the car full of bored, bat-wielding teenage morons and commence playing a slightly different game, namely administering some swift and well-deserved vigilante justice involving the baseball bats and the punk's prized car's (or, as often as not, the punk's parent's car's) fenders, headlights, and windshield, and perhaps also the punk's kneecaps for good measure.
Footnote 1:
VT_hawkeye's right.
My point was that although vandalism is illegal in general and mailbox destruction is illegal in particular,
there's no specific law or enforcement mechanism stopping kids from driving along thwacking mailboxes at night; they can and do get away with it all the time.