I wonder if the click-through rate on those popups is worth the number of users who just close the tab? There must be some metric somewhere that deemed it better to shove a pop-up than just have something at the bottom "hey if you liked this you can subscribe for more".
Apologies! I'd actually JUST added that (at about 2:30 in the morning). I'll remove it for now and do some testing. Didn't expect it would be intrusive on mobile - sorry!