The constant churn of new video formats is one possible reason. If YouTube doesn’t convert all their old videos, they may become effectively unplayable (see for example how many 80s and 90s AV formats have vanished). But even if they do convert all their old videos, repeated transcoding could gradually turn them into mush anyway.
Those problems could certainly be avoided or worked around if YT takes sufficient care, but maybe they won’t have the right incentives to care continuously for the next 1000 years. I think it’s a much harder challenge than preserving paper and vellum artifacts.
>The constant churn of new video formats is one possible reason. If YouTube doesn’t convert all their old videos, they may become effectively unplayable
YouTube already does an encoding pass even with the most "perfect" h264 source. I wouldn't worry about video formats more than I'd worry about when YouTube shuts down.
We're going to need an incredible increase in storage density before we can think of doing a full replica of YouTube (I wonder if we'll ever have the processing power to de-dupe the amount that's uploaded).
Those problems could certainly be avoided or worked around if YT takes sufficient care, but maybe they won’t have the right incentives to care continuously for the next 1000 years. I think it’s a much harder challenge than preserving paper and vellum artifacts.