Affordances and auxiliaries peculiar to one verb are often found with other words derived from it.
Since subscribe takes to as a transitivizing preposition, so does unsubscribe.
- She had subscribed to it for years.
- She unsubscribed to it after they published that letter.
However, since unsubscribe has the negative sense of reversing a subscription, and cutting a connection -- in other words, moving away from -- the general ablative transitivizer from is also sanctioned, although it's not correct with subscribe.
- She unsubscribed from it after they published that letter.
- *She subscribed from it after they published that letter.
- She was divorced from him shortly afterward.