Ever compare a Blu-ray to the same content over streaming? It's not even close. Unlike vinyl records, Blu-ray is vastly superior in quality to alternatives.
In case you're asking "why", it's because your "4K" stream is compressed to hell and back. Your home internet connection doesn't even have the bandwidth to stream the quality of a BR.
> Your home internet connection doesn't even have the bandwidth to stream the quality of a BR.
This has not been true for most people for a while now. Even the high end of 4K blue rays tops out around 100 Mbps, which is achievable on pretty much any broadband connection.
A UHD Bluray tops out at about 150Mbps, most home internet is capable of that. It would just cost too much for the streaming services to support it.