You might be surprised to learn that videos and many images are broken down into brightness + color vectors. Brightness is typically done near the resolution of the image (eg 4K) but color is often 1/4 of that. That’s literally blurring the picture.

…Why would you write a comment like this assuming I don't know what 4:2:0 is when I know what a wavelet is?

It doesn't have the same effect because the original high frequency details are correlated and so they're preserved in the Y channel.