At least sending spam is basically free for them, so any returns at all are gravy. In your snail mail you're probably getting mostly paper advertising which go

At least sending spam is basically free for them, so any returns at all are gravy. In your snail mail you're probably getting mostly paper advertising which goes straight into your recycling bin, and those people have to pay something even if it's "not much". And it's still apparently profitable, or else they wouldn't keep doing it. Just hang out on NextDoor and you'll see how dumb some email users are. And then if you consider all the ones who are too dumb to even get on NextDoor, and you've got a target-rich environment there.