It’s a good question. For whatever reason, consumers have told content providers that they’re not really interested in physical media anymore (despite the fact our internet infrastructure is pretty bad, way overpriced, and regulated poorly by our government) and it seems pretty plausible that 4K is essentially where physical media stops. While this is a bad thing in a lot of ways - the removal of the cost of producing physical copies could remove a barrier or two.

Of course, the cost probably isn’t a very big concern as to why the original versions aren’t being released - but it would probably be easier to make them a digital only release. Digital only releases are likely what we’re looking at in the next 10 years anyway.