Because YT reserved /playlist and not /playlists. They also haven't reserved /watchs or /watched.<p>People will quickly realize that /playlists loads some random channel they don't care about and will click away.
Because youtube hasn't siezed it from them yet?<p>What I'd want to know is what percentage of netizens* even know that you can just add stuff to a url willy-nilly.<p>* as I type this word, the cognoscenti can literally hear my bones creak