Did YouTube do away with 4K?

Searching for 4k (4096 horizontally by 2306 or some other number vertically) videos on Youtube today, I realized there aren't any. Including those that certainly were 4K last time I watched them - probably 6 months to a year ago.

If you are interested in videos with resolutions higher than 1080p, you may remember that YouTube announced support for full 4K resolutions in their official blog post of July 2010, "What's bigger than 1080p? 4K video comes to YouTube". No subsequent blog posts seem to announce any changes to supported resolutions. In my blog post shortly after YouTube's announcement of 4K support, I pondered about the reasons YouTube decided to support 4K given the extreme rarity of computer systems and devices that were capable of displaying it. My guess was YouTube was future-proofing itself and playing with possibilities.

Here is the playlist I assembled of 4K 2K clips. In quite a few of them, you see the posted resolution of 4096xN where "N" is the vertical resolution number usually between 2160 and 3072. All of these videos now only play at 2048x1536. You can verify that by right-clicking on the video and selecting "Show video info".

Do you know why and when YouTube decided to stop supporting full 4K videos?

(A 2K video sample. To watch it in full 2K glory, click "Play" first; then select "original" in video settings - the wrench symbol in the bottom right of the player box. Make it full screen. Pause and wait till it buffers if you don't have a particularly fast Internet connection. It helps if your monitor is large with a native resolution higher than 1080p.  How's the viewing experience?)

P.S. 4K is not the same as 4096P, and 2K - is not 2048p.  In "4K", "2K" and similar designations, the number such as 4096 stands for horizontal resolution, i.e. 4096 pixels horizontally by 1536 vertically.  Designations such as 1080p (along with 720p, 480p, 1080i, etc.) refer to vertical resolutions (e.g. 1920 horizontally by 1080 vertically).  In the old analog TV days, signal resolution was also measured horizontally, i.e. in the number of vertical lines, like today's 4K.