So? You don't need a proven causal pathway to state that a glass heads towards the ground every time you brush it off a table.

Scientifically you do, otherwise you can’t claim that lack of sleep was the cause of death. It could be an artifact of how the experiment was run, or any number of other factors.

It’s not a small quibble to point out that the central argument (“animals need sleep or they’ll die”) may be mistaken.