I’ve realized the other hideous incentive to not cancel your Humble Monthly. When you go to cancel, they offer you a discount on the next month to stay.
So it is better to stay subscribed and just pause every month until you find a month that you do want, then go to cancel and “agree” to the offered discount to stay. I’m sure Humble doesn’t mind this tactic either, as they’d presumably rather have a person pause every single month than outright cancel. A paused subscriber is still a subscriber (which boosts the numbers they can show publishers), a paused subscriber is probably considered more likely to unpause for a new bundle than a cancelled person is to resubscribe, and a continually pausing subscriber may forget to pause some month and accidentally buy a bundle.
I’ve been on the verge of cancelling for several months, but have stayed (paused) for that discount chance.