Researchers call it the "video deficit effect": children under three learn a skill more slowly from a video than from a real person or object showing them the same thing, even when the video is well made.
A block does not have this problem. When a toddler stacks a block, every part of the action the reach, the grip, the wobble, the fall is real feedback their brain can use immediately. That is why open-ended toys like blocks, stackers, and shape sorters punch so far above their weight in early learning.
