There are some of us that think the distraction economy is making the world a worse place.
OS notifications have a higher participation rate than side-bar ads because 1) nobody has learned to tune them out, and 2) theoretically speaking, these are the things we opted not to filter out, so we are more inclined to peek.
I know people who will stop mid sentence of an interesting conversation with you to figure out why their phone is chirping at them. I'm sure you do, too. It's painful to watch even when it's not you.
My reaction to "it's opt-in" is a little bit like my reaction to "tobacco is opt-in". It's not reassuring, maybe even a little troubling. The best reaction you can expect is, "And?"