Hi,
yes, I see your reasoning behind this.
I would assume the reason of doing so is related to performance - on very large communities the automatic calculation (after every edit of a Badge) if someone should receive a Badge could cause problems. I had a conversation with our team to find out more about the reasons, however I was informed that it would take some time to properly investigate this. :/
I agree with you that this way of processing changes in existing / creation of new Badges would benefit the re-activation of users. This surely is something which we will keep on our radar to improve in the future. Hopefully we can touch this when we are working on Badges again.
We will actually work on Badges again very soon, as stated in
my reply to the popular idea to manually grant Badges to users. This improvement will most likely also help you to achieve your goal to target inactive users, at least until a certain degree.
I will keep an eye on development to check on the process of assigning Badges automatically once this happens, to make sure they will look into this. If I learn the answer to your question on the way, I will share it here with you.