No offense, but you seem to not understand how blu-rays, video files, and film masters work...Ill try to give you the gist of it. Been a while since Ive had to explain this to anyone (used to do it a lot for family members) so I may be a bit rusty.
Current blu-rays cant render a 1080p file in 4K anymore than a dvd can render a 480p file in 1080p, because the video file on the disc has a finite amount of resolution/pixles/data. A blu-ray player can upscale the image to 4K but thats not the same as having a true 4K file on the disc. Just like upscaling a 480p DVD to 1080p is not the same as a true 1080p file. A dvd upscaled to 1080p can never look as good as a bluray with a native 1080p image, and a 1080p blu-ray upscaled to 4K can never look as good as a native 2K, 4K, or 8K image.
So if you want a true 4K image or any resolution higher than the 1080p file on the blu-ray you have to go back to the Master copy of the film that the studio has which is usally 2K, 4K, or 8K and create a new copy at whatever resolution current home video tech can handle. Then you put that higher resolution file on the disc. These higher resolution files require discs with more capacity (more layers) and better codecs. To read these discs you need new hardware (players).
Thats just the way it is.
Now, granted you could say "Well then the hardware should have been future-proofed." It should have been but it cant be. Bluray was patented and created by Sony and it and a group have control over blu-ray and its designs and codecs and specs and yada yada yada point is that to maintain uniformity and capatability across many releases and many different players from many different companies and studios there are standards decided on for the format. Until Sony and the others decide what that hardware and software standard is companies cant and wont begin producing hardware and software according to those standards. The specs for 4K players and discs arent finalized yet so companies cant begin making 4K players or releasing software updates yet and there was no way they could have future proofed their hardware and sofrware for 4K before those specs are finalized.