first of all I totally get why this would be annoying. My inbox is full enough without someone adding in an unsolicited email regarding a job I never asked about. I seriously, totally, completely get it.
But here's the thing. Shitty as it is this is still how hiring works much of the time in our industry. And frankly that email in someone's inbox is either the town drunk wearing nothing but a barrel and puking on their shoes or a knight in shining armor saving them from the dragon's flames depending on that person's set of circumstances.
Companies grow so quickly these days that no one can really afford to prize etiquette over expedience (ethics over expedience is different- no one gets to excuse themselves from ethical behavior).