It's not just that piracy is common, it's that there's so much free (mostly ad-supported) stuff on Android that people don't really know what they're downloading. If they get all their APKs off of some random site they won't even realize that it's supposed to be a paid app. It also makes it a lot easier for someone to superficially modify the app and put it on Google Play and it won't be immediately obvious that it's really our emulator.
This means that some people who would be willing to pay for it won't because they have no idea it's for sale, and that the volume of people looking for help using it will increase because it'll include people that don't know they're pirating it.
The license check enables anti-tamper measures so it's easier to know when someone's using a cracked version and it signals that to people on a repository. So for example there are cracked DraStic APKs on Aptoide but the comments sections are filled with people complaining about them crashing. That helps boost the message that it's not a free app. It's far from perfect but it's at least something.
With games it's kind of common knowledge that they're supposed to cost money and it's going to be really obvious if someone tries to pass it off as their own thing. So the people who pirate it are much more likely to be limited to those who were determined to do so deliberately.
There wasn't ever really an initially sales wave, just a very gradual slowing down of sales, with some bumps when we update versions.. so honestly we don't really want to turn away from what we're doing there any time soon. Sure eventually things will dry out, or it could be removed from Google Play for whatever reason, or Google Play could stop working altogether.. I don't intend to just let it be gone forever if something like that happens. But for right now I don't see us removing the license stuff any time soon.. This is obviously a self-serving decision, making it DRM-free would be better for users (as would making it free altogether, and open source at that), but the people who are interested it buying it only w/o DRM are a relative minority.
The Pyra version will be unencumbered/free (as in beer) so that's about the best I can say to wait for for now. Sorry