People often think that old video must be stuck to standard definition (or worse), because they're used to seeing it on NTSC/PAL broadcasts, VHS, or DVD.
The reality is, these things were captured on film, and there's no reason you can't scan the film in high definition resolutions. Film is an analogue medium whose upper bound for resolution is dictated by the film stock and grain; 35mm film is sufficient to produce modern 4K scans and was one of the most common stocks in analogue video production.
If anything, modern 1080p/2160p scans of old film bring the material much closer to how people with projectors originally saw the media, instead of a blurry scaled down version made for old television.
If I may provide my favorite example, check out Wizard of Oz in 4K. It's from 1939, in full color, and holds up wonderfully well. The 4K transfer allows you to really appreciate the set design and makeup especially.
