Cost. If you've already got an old, cheap server lying around, then having an 8 TB box at home is very cheap. Say, $15 a month for Mullvad + power usage. Reputable seedboxes seem to be in the range of ~$60 a month for 8TB of storage. Obviously, if you want to scale beyond that, it's as simple as adding another 8 TB drive to your box at home, whereas a cloud seedbox would nearly double in price.