They are already there, and someone is paying for the storage and bandwidth for what's already there. Asking for random people to start pulling videos from YouTube and uploading them to someone else's server is going to very quickly make that server go away.
And yes, I have tried Peertube. My experience is when I click a Peertube link from Lemmy, 9/10 it is a dead link.
They probably thought you were me, I got blocked above for making a similar point that you'd also made (although I think you did a better job of making the point).
Apparently pointing out that Peertube still has quite a way to go to meet YouTube's feature set just shows incompetence.