@Necronex666 brought up a very important distinction...
There's really no reason for this to be the case for longer than necessary...
I focus in on that specific phrase because the way "necessary" is defined here affects the behavior of security devices that have been uninstalled, but not unscanned from a hub.
I don't want to go into too much IC detail. That being said, everything I am about to say comes from publicly accessible help files and examining devices. None of it is gated behind skills.
Based on previous conversations with staff, my understanding is that "is necessary" to keep devices connected to hubs to deter theft. If it were possible to easily reset / unscan devices from hubs, then to a certain extent the game would devolve into a constant back and forth of people stealing each other's gear. Ultimately, the character with the highest skills in the game would just "own" all of the other devices because nobody could touch them.
I think @necronex666's suggestion about having the devices become unlinked after a period of time seems reasonable on the surface. It might be even better to allow the owner of the hub to voluntarily 'unscan' any disconnected devices. Being able to unscan would all people to clean up their monitor feeds and remove all of the 'lost' devices.
The down side to that approach is that it does not serve to deter theft. In the current system, someone who steals a piece of security tech cannot use it. Therefore they have to get rid of it. They do not hold onto it for very long and it 'disappears' into the economy.
If players know that their stolen tech might become valuable as soon as the owner gets around to 'unscanning' it, then we have created a situation where players have incentive to stockpile a bunch of expensive gear knowing that, sooner or later, they will be able to reuse it themselves, or sell it 'like new'.
That is the challenge as I see.
I do not necessary know what the good middle ground is that allows network owners to clean up 'lost' devices, while at the same time still deters theft and keeps a portion of the game from devolving into two or three characters spending every waking moment trying to steal each other's gear.