Because running a business and trying to contact you is such a terrible thing. Instead of adopting a self-entitled stance that I have the right to not be disturbed and any violation is an attack on my ego driven need for individual sovereignty, I have learned to respect and even root for the small businesses trying to make a dollar for themselves while everyone else is busy wasting their life away being wage slaves for giant soulless corporations. I don't get mad, I evaluate the email if I'm interested.
So you (or the people running your mailbox) don't filter spam? At all? Really? Or do the dollar signs in your eyes shift your perspective about the handful of spam that gets through the automated filters?