As a user, those emails have sometimes had a negative effect for the company emailing me. Something they send me reminds me that the program exists, that I'm still paying a monthly fee for it, and that I really don't use it very much at all.
But in all fairness, I doubt anything they could have said or offered would have changed my mind at that point. It was just a matter of when I cancelled, not if.
I think your last sentence is important - you were already gone, it was just a matter of time.
If the numbers work such that losing 1% of customers means keeping 3% i.e. the email prompts them to leave/stay respectively, then it's worth sending.
Getting rid of low-value users - in this case those not playing - can have long term benefits of focusing the business on getting more custom instead of getting comfortable on revenue that may disappear at any point.
The reason for emailing you could also be to find out why you aren't using the app. Even if one ends up closing the account as a result, the information gained is valuable for improving the product.
But in all fairness, I doubt anything they could have said or offered would have changed my mind at that point. It was just a matter of when I cancelled, not if.