At the time of writing, package bug subscriptions have existed for roughly a year. Currently any bug reported about Ubuntu's "linux" package has 31 indirect subscribers, of which 8 are deactivated users.
Active users may subscribe to or unsubscribe from a package over time, but by definition deactivated users don't do anything, including unsubscribing from anything.
So unless something is changed otherwise, five or ten years from now the vast majority of subscribers to the average package will be deactivated users. This will make subscriber lists steadily less useful over time.
This problem applies not just to subscribing to package bugs, but also to individual bug reports, individual branches, a project's branches, a project's translations, or anything else.
One way of fixing this would be, when a user has been inactive for three years or so (so they've had plenty of time to change their mind), unsubscribe them from everything they were previously subscribed to.
Maybe we should just hide those inactive users in the web ui. Marking as low as this is not a problem until 5 or 10 years from now :-)