In a sense something like 3Blue1Brown or a good DIY channel is almost a modern equivalent in terms of content but the thing these old documentaries (not to be overly patriotic but often British ones) have that most (almost all, really) YouTube videos have is the expertise and creative bottleneck of being made by a proper TV studio.

Bottleneck I say? From limitation and oversight comes restraint and clever tricks, and that is a good way of making good media.