While the cost of video delivery is negligible, there are definitely increased costs for delivering 4K video.
It takes more storage on the CDN box, and also takes more bandwidth on the outbound network port. That means you need more CDN boxes and more hard drives, which means renting more space and power and cooling. Also, you need to be closer to the customer for the 4K video since it's so high bandwidth, so that means more CDN deployments.
You also have to get the 4K video to the CDN, which is more costly because of the extra copies and the large files.
You also have to create all the 4K video files for all the devices, which takes a lot more processing time in the video pipeline.
You also need higher res files from the studio, so of course they charge more for that since it costs them more to move the large files around, store them, and create them in the first place with better camera equipment and editing equipment.
It takes more storage on the CDN box, and also takes more bandwidth on the outbound network port. That means you need more CDN boxes and more hard drives, which means renting more space and power and cooling. Also, you need to be closer to the customer for the 4K video since it's so high bandwidth, so that means more CDN deployments.
You also have to get the 4K video to the CDN, which is more costly because of the extra copies and the large files.
You also have to create all the 4K video files for all the devices, which takes a lot more processing time in the video pipeline.
You also need higher res files from the studio, so of course they charge more for that since it costs them more to move the large files around, store them, and create them in the first place with better camera equipment and editing equipment.