Maybe it's due to higher quality cameras being used more than the resolution.
So true. The source matters so much more than the end resolution. I've seem some really good 144p videos and some really atrocious 1080p videos on YT. If the source sucks the higher resolution isn't going to help and at the same time a low resolution can still look great if the source is pristine and clean, just don't stretch the video out too much.