Why should that one situational towerdive be worth an item slot when your tank can just tank the turret? The stats aren't good on any towerdiving champ either. I see that the active might be slightly useful, but I can't think of a situation where it would warrant wasting an item slot.
If they buffed turret damage (Epically to TANKS as they stand under it and not take any damage now...) it'd be a very nice item that a lot of supports would buy.
but right now..
: Ahahaha Tower tickles...
I'll occasionally buy it on 
just to help out with catching people and keeping from taking any turret shots if I dive. Always best to stay as healthy as possible, those two turret shots may be your death!
To rub it in that you're living. To force the turret to retarget when you can't leave it's radius in time. To save your dumbass carry when they won't leave and you need them to not die.
Basically, if you can't juggle aggro, it's occasionally useful. But not really.
I like it on Leona support just because of how often she wants to dive. Not having to tank the turret is often tactically superior. It lets us assault two turrets in one push, leaves me strong enough to cover a retreat, etc.
Riot balances things perfectly. this is a sport. If it was unbalanced if might be considered only a game.
Turrets do so little damage now that there's really no point in this item.
