Sound and power consumption. At least in my case those are important if I was going to store data at my mothers house. Power consumption might not matter that much, but HDD sound definetly does. And even with spinning rust hardware cost would be somewhere around 250€ compared to ~20€/month of cloud storage.

YMMV, in my scenario it's just easier to use a cloud provider.

Hetzner will increase their prices by April, still a good value

https://www.hetzner.com/pressroom/statement-price-adjustment/

By your parents a computer and put it on their network and back up locally and remotely on their system. Bonus run immich for them also.

I get all my back up redundancy but helping others host.

I think they are analogous. If you like your setup keep using it ;)

JFYI - after many years of trusting Borg with my backups, I found Kopia to be MUCH faster, in both snapshots creation time and browsing/diffing. I backup my whole home every 6 hours, so going from ~20min down to ~3min is an appreciable win. There's also a web endpoint to Kopia that may make backing up on the go easier when you can't trust your tunnel to home.