It is extortionate because it is a digital stream which is more expensive than renting a new release Blu-ray. A digital file is able to be rented to tens of thousands of people simultaneously where a physical video store has to buy dozens of copies of the Blu-ray to rent to dozens of people simultaneously.
The business has massively reduced overheads (even considering the need to pay for commercial CDN and IT infrastructure) but instead of making their product offering more attractive to consumers as a result they continue to try and milk every cent through PPV. It is extortion.
I think your criticism of StuffPix is unfair in this regard. You need to level your criticism at the studios that PPV players sign the distribution agreements with. It would be commercial suicide for StuffPix to offer a flat rate for viewing and have to pay a fee per viewing to the supplying studios. It would only take 3 new release movies for StuffPix to be eating a loss on something like $10/month for unlimited PPV. You want new releases on a flat rate? Isnt that something Neon offers? And hows that model working out?
Someone like Netflix with deep pockets (sic) could offer new releases on a flat-fee basis but then they'd have to disclose to the studios how many times a movie was watched (unlikely) and could probably drive a better deal on 100 million potential viewers. But the studios would equally say - if you dont pay the fees we want then you dont get our product. There are plenty of other PPV operators that have sucked up the terms on offer so why would a studio change its profit maximising formula?