Just want to add on clarification that this doesn't mean "they look bad because everything looked bad back then", but rather, they were designed to look good^1 on CRT displays because the graphics people were used to working with CRT artifacts, so when different display technologies arrived that didn't behave the same, the CRT-targeted graphics didn't look as good as they were meant to.

It basically came down to pixels bleeding into neighboring pixels in a way that created gradients between pixels. So while the pixels themselves were still limited to the ridiculously low resolutions of CRT TVs (which basically didn't change since broadcast TV was a thing), they could simulate a higher resolution for the shading with those subpixel gradients.

1. Though note that this "good" is still relative to how good things were able to look at the time. The resolution is still way under what you're used to today.