I agree that a multithreaded borg could utilise resources better, esp. IF you have a lot of changed / new data to back up.
But OTOH, for many users this is primarily the case for the first backup, but not for their daily / hourly backups when most files are unchanged - for that, I guess speed is I/O bound and all your CPU cores won't help you with that.
So for N-1 backup runs, it just works good enough already for many users. And for that 1 initial backup, some patience helps. :-)
Implementing MT is planned since long, but due to the above, other stuff had higher priority.
But OTOH, for many users this is primarily the case for the first backup, but not for their daily / hourly backups when most files are unchanged - for that, I guess speed is I/O bound and all your CPU cores won't help you with that.
So for N-1 backup runs, it just works good enough already for many users. And for that 1 initial backup, some patience helps. :-)
Implementing MT is planned since long, but due to the above, other stuff had higher priority.