Obviously I can't see your total numbers, but Google Play lists it as 1 install. Ad revenue depends on several factors, and certain people are worth more than others.
However these sorts of ads never pay well regardless; if you are planning on having this sort of passive ads you will need substantially more traffic.
You would be better off using various other monetization strategies for the time being.
Ads are fine, but few pay a lot unless they are implemented in a natural feeling way; banner ads are trash and tend to make players annoyed and less likely to spend.
There is one very simple and obvious change you can make that I can guarantee you will get you more money than these admob ads, and most players probably won't even realize its an advertisement. I've been doing extremely well and where your "game" is sort of like an arcade, it would fit in better than in mine.