The only reason you’d ever need a UHD and BD dual release is so you can compare both discs and see how awesome the HDR is lol
I can’t say I’ve not bought a UHD because it didn’t have a Blu-ray in the box as well haha. HOWEVER, there is a trend particularly in America with big studios they release a UHD with no special features on the 4k disc and you don’t get the Blu-ray in the set, in the UK that same release will include the Blu-ray with the special features… so in that case I can see the point. The Exorcist was like this in US vs UK.