Whoever still buys Blu-rays anyway? Isn't it a dead market already?
Streaming services' bitrates top out around 40 Mbps (4k UHD on Apple TV), and most services are actually closer to 20 for 4k, often even lower. 4k UHD Blu-Rays have up to 128 Mbps bitrate. The quality difference is evident, including in the sound. You can see compression artifacts in dark scenes on streaming, and jagged lines in color gradients. The simulataneous dynamic range of sound (some things being loud while other, quieter things are audible on other speakers at the same time) is lower on streaming. And on top of all that, the quality is inconsistent, and the stream will drop into a lower resolution for no apparent reason.
I get the sense that the market is drying up, but I hope it doesn't, because the quality of streaming is legitimately worse. The discs are currently the only way to get uncompressed quality, unless I guess if you find a torrent with a rip. But that would be a 50-100 GB download, for one movie.
Also, when I buy the disc, I own it. It's mine forever, in its definitive edition. No scene cuts/edits for political or monetary reasons are possible, and streaming services cannot yank the movie and prevent me from watching it.
It is worth noting though that the content on BD/UDH-BD is not uncompressed. They're still compressed using h.264/h.265/VC1/.. for video and DTS, AC3 and various other codes for audio. It's just that you get a much higher bitrate from the BD compared to streaming. This does make a difference on bigger TV, especially since our internet connection is not as good as it should.
As for the future, when world eventually transitions to H.266 or some other next gen codecs, and at the same time internet speeds keep increasing, this whole debate is largely theoretical. You will be able to stream UHD movie at half or less of of bits that it would take today when compressed using h.265, using internet connections that are n times faster than those we're using today.
Call me old school, I still like owning those BDs. But it's hard to imagine future where they would age very well (compared to quality you are likely to get from streaming services).
Plus a Blu-Ray off eBay or CeX is usually half the price of 'buying' a film to stream, can be lent to friends and family, and is something that I meaningfully own into the future (not only until the service I bought it from goes bust, locks me out of my account, etc). The fact I can rip them with MakeMKV if necessary is handy too.
Why? I'm fortunate enough to have gigabit symmetrical fiber, so streaming isn't an issue. That said, when viewing content on higher quality TVs and sound systems, there's a very perceptible improvement in both video and audio quality compared to streaming. For example, on my 65" LG C9 OLED with a Klipsch Atmos system, the difference is immediately noticeable.
Even with dedicated streaming hardware like new generation Apple TVs, which offer 4K streaming with Dolby Vision/Atmos, it still doesn't quite compare to physical media. Ditto for the native LG apps with identical options.
Of course, there are downsides. Good luck finding UHD content on physical media. Redbox doesn't offer 4K discs in my area, and local stores rarely have physical media in stock. Even with physical media, there's other annoyances--e.g. the Xbox One X produces a loud hum as the disc spins, not to mention the delay when seeking/skipping around.
That said, for rarified material such as Blue Planet (or anything by Attenborough)--or movies known for their sound quality like Mad Max--physical media can be sublime.
Unless streaming sites up their game, we'll see a drop in movie image quality everywhere except cinemas.
Note that in the US at least, owning a physical item can be legally important due to things like the first sale doctrine.