Ads appear to be the only way to monotone certain cervices or products which people are otherwise unwilling/unable to pay for.

Part of it is friction and fees in payments, not just customer willingness to open their wallets.

This puts a practical floor on any $X/month model.

Which is the vast majority of entertainment/news/media/anything non physical at this point.

I think the difference there has nothing to do with what people are willing to pay for, and is simply because of differences in the marginal costs of delivering physical and digital goods vs what they bring in with ad revenue.

If it was possible to turn a profit by showing ads to people eating burgers, we'd have restaurants hawking the most addictive, free burgers on the market.