They're the ones that will have the logs and information and will know how the service is and isn't being used. Not you, (unless you happen to be an actual kernel.org admin?)
Just because it doesn't make sense to you, does not make it stupid.
Mirrors almost universally use rsync, not FTP.
I mean FTP mirrors, that offer an 1:1 FTP directory mirror.
Literally no one does that. rsync-over-SSH is often used for this, sometimes plain rsync, sometimes custom stuff running atop SFTP (which is a completely different thing from FTP(S)).