First of all, i would like to say hi. Anyway, there are some inaccurate information here on this article that i like to point out. Even at 128 mbps, it still not enough bitrate to store uncompressed 4K videos. Not only that but 128 mbps isn't even enough to record or store in "2K" or 1080p videos in uncompressed bitrate. Its possible to store 480i uncompressed at 128 mbps.
Because 720 x 480i @ 4:2:0 Y:Cb:Cr sampling @ 8 bits per channel only take roughly about 125 mbps of bitrate in uncompressed data. That means even at 128 mbps, it still very compressed for 4K videos. But compares that to online streaming (assuming you are correct that its 15 mbps), it still a lot lesser compression.
Another inaccuracy you said is that DVD is 7 GB single layer. DVD actually store 4.7 GBytes single layer, or 8.5 Gbytes Dual layers. DVD also supports dual layers too beside Blu Ray.
You are correct that regular Blu Ray Disc single layer is 25 GBytes and 50 Gbytes Dual layers.