Seriously, what the fuck? I thought it was some kind of user interface glitch so I looked it up. Nope, they're A/B testing this shit.
Found this brilliant statement by Youtube on the matter:
Now note that we are deprecating one sorting option and that is by oldest video at the channel level. But don’t panic, you can still view the oldest video of a channel, by scrolling through it’s content’
Oh, yeah, just scroll to the bottom. Silly me, I guess I'm just a stupid idiot for not realizing the option was redundant since I can simply take the time to scroll through potentially thousands of videos.
Why are silicon valley tech people such freaks?
It's Google. That's why. They don't want you opening a folder, and then grabbing a subfolder and paging through entries.
They want you to search.
They want you to always search.
If YouTube hadn't been bought out by Google you'd have pages of videos. This is Google's own project to make sure YOU ALWAYS SEARCH.