Wow.
It's just incredibly slow.
In my case it hangs after those lines for about an hour before producing any additional output in the PowerShell host or writing any files to the backup location.
As documented elsewhere, both the user running the Backup-SPFarm cmdlet and the user (service account) running the database service need permissions to write to the backup destination. But it won't even display errors about that until after the long silent hang period.