They probably don't. Forced ad viewing is fundamentally dishonest: they can force the user to watch the ad, but they can't force him to pony up for what is being advertised.
I would say Facebook ads have sold me on a few things. But they are not full page, I can easily identify them and move past should I chose and at times were actually relevant to what I want. How come YouTube ads try and push the dumbest shit on me when they have all my data and know all my searches yet I’m getting ads for stuff I would never buy. So I propose google cut back on some of the video ads, force the video being watched to slim up a bit while no video ads of relevance pop on on the side.