That's already configurable during the screening phase, before it gets to the AI. It can be configured to only look at authors who have been active within a specified number of days. I have experimented with different options over the course of time, but right now I'm not enforcing any restrictions on that (as you correctly noticed ;-)).

My thinking on setting the inactive authors to be eligible (for now) is that (1.) if they happen to sign in and see the rewards sometime in the future, it might be a motivator to bring them back (and after the first person discovers their "air drop", it might bring others back, too); (2.) In the worst case, it's equivalent to burning the rewards; and (3.) a lot of our interesting content was created by inactive authors, so it can still help to draw search interest and bring readers.

FYI, the full list of potential parameters (so far) is here. It can also screen based on things like delegations and characteristics of the follower network.