Video streaming platforms are not generally running on a pay-per-view monetization model. A few offer this, but the vast majority of them are offering it at $15-20/months for unlimited streaming. 4K video uses quite a bit of bandwidth. Low end is something like 15Mbps. That’s ~7GB/hour. Or, $0.385/hour at these proposed rates. Doesn’t take long to start approaching the cost of the streaming services charge.
The easy answer there is to limit French residents to 720p rather than 4K for the $15 plan.
720p AV1 is about 700mb/hr, so about an order of magnitude less than your 7GB/hour.
It's not like a 720p limit for tax reasons is any worse than a 720p limit for lack-of-Widevine-support reasons.
And for households with kids, it's easy to imagine that turning into 30 hours a month, or $12 by your reasonable estimate. That's not a huge number, but I'm sure that'd push almost any streaming service into negative territory. I don't know what the average service's profit margins are, but highly doubt any of them could absorb that kind of hit.