Explanation
Shares matter disproportionately because each one is a distribution event rather than only a signal: the video reaches a new person through a route the platform did not choose. That is why content designed to be sent to a specific person, the this is so you videos, outperforms its raw view count so consistently.
It is worth separating sends, which are private and go to one person, from reposts, which are public. Sends indicate the content is useful or funny to a particular relationship. Reposts indicate somebody was willing to attach their identity to it, which is rarer and worth more.
The common mistake
Reading a low share rate as a quality problem. Plenty of genuinely good content is not shareable, because there is nobody obvious to send it to, and that is a property of the subject rather than the execution.