With those HD + UHD packages, only the UHD disc contains the HDR color space. I bought The Last Jedi when it came out and I never even bothered to watch the HD disc because it's only in SDR. It's a useful thing to sell to people if they haven't upgraded their TV yet; they can get the movie now and have the UHD version available for later once they upgrade without having to buy another disc.

As an aside, it's kind of a shame that 1080p HDR has never been a thing. Smaller TVs that support HDR at 1080p would be great value. Of course, the support for HDR on the base PS4 and Xbox consoles has been a great thing for 4K TV owners, but the HDR has always been part of 4K. I'd just love to see HDR at a lower price on sub-50" TVs.