Just did a quick test 320x200x8bit grayscale PNG (couldn't quickly figure out how to get 8bit color pallet) compressed to ~15-40kB. Multiply that by 60frames a second (or whatever odd framerate historic hardware used) and 120seconds and you get 200MB. Not completely impractical, but I wouldn't call it trivial amount of space. And if you find any demoscene collection providing losslessly compressed videos let me know. All I have seen is original executable+youtube video (which suffers from compression artifacts). And I doubt many demoscene website maintainers are eager to increase their storage and bandwidth costs 100x.

Fair, it’s indeed a shame if there aren’t lossless or very-high-bitrate lossy recordings available. A literal sequence of PNGs is of course an upper limit, using temporal coherence (of which there’s a lot of) would shrink the size to maybe a few tens of megabytes. But of course there aren’t many lossless video formats in common use because it’s a rather niche use case outside mastering and archival. There’s lossless H.264 and H.265, and IETF’s FFV seems pretty well-supported too. Not sure if browsers support them though.