It's worth playing the "what if everyone did this" game: I have ~20 apps installed on my phone. If everyone sent 1 promotional message a day, I would be getting 20 per day. Which would mean more than one each waking hour. That's about as many notifications that are actually of use to me each day, and that amount of spam would effectively render notifications useless to me. I'm very thankful I can disable notifications for apps.