Why does teleport replace the first node of the container in ssr?

[baiwusanyu-c]

I noticed that the first node of the target container will be selected when the teleport is hydrating, and the document specifically states that the teleport should only contain the content of the teleport when ssr is used(see). I don't know why it is designed this way. Because then in the code target.firstChild will always be null

[baiwusanyu-c]