Who should build a BotRK?

Everyone seems to love the Blade of the Ruined King lately but I've seen it being build om some adc's who quite frankly don't seem to have much use for it. I've seen Ezreals rush it as a first item. I understand that it's a nice item on Varus since having extra attackspeed helps with your W, and that it's nice on Tristana since basically nothing scales with AD and you're an adc who's basically all about the basic attacks.

So can anyone tell me why adc's who actually scale with AD are rushing this item? (Ezreal etc.)