There's a lot of archival video that is just terrible. Digital video compression issues have damaged a lot of old footage that's gotten shared over the years, especially YouTube's encoders. They will just straight up murder videos to save bandwidth. There's also a lot of stuff that just doesn't look great when it's being upscaled from magnetic media that's 240x320 at best.

However, there's also a lot of stuff that was bad to begin with and just took advantage of things like scanlines and dithering to make up for poor video quality. Take old games for example. There's a lot of developers who took advantage of CRT TVs to create shading, smoothing, and the illusion of a higher resolution that a console just wasn't capable of. There's a lot of contention in the retro gaming community over whether games looked better with scanlines or if they look better now without them.

For example.

Personally, I prefer them without. I like the crisp pixelly edges, but I was also lucky enough to play most of my games on a high quality monitor instead of a TV back then. Then emulators, upscaling, and pixel smoothing became a thing...