Hey guys, developer here.
It's basically because Android users in general don't want to spend money. Because the platform is open and the users of Android tend to be quite tech savvy, they tend to not want to pay money for software anymore, despite the fact that it's so cheap anyway. It's not just piracy that does it, even the non-pirates on Android tend to gravitate much more towards the free software, and don't tend to buy the in-app purchases, and hell, they've likely rooted and installed an ad blocker as well, so the game makes literally nothing. In developer circles/communities generally it's agreed that "Android users don't want to spend money". A lot of the big publishers literally just say "don't bother with Android, there's no money to be made there".
The thing is, it's not ALL about the money. As a developer I love what I do and heck, I'd do it for free if I could, but you have to put food on the table and pay the bills, and it's just not reasonable to spend evenings and weekends developing after working in some other job all day, but if you forget about the money, it's the fragmentation. You could make an all-singing, all-dancing game with great graphics running at 60FPS, and then get a bunch of people request refunds because it doesn't run properly on their phone, and there's no indie developer in the world who wants to get every single Android device for testing on.
So to cut a long story short, Android is difficult to develop for due to the fragmentation and the users don't spend the money to pay for the extra development and testing time that it requires.
Another thing to consider is, for example, a developer might bring you a simple retro sidescrolling platform game with jumping puzzles, power-ups hidden in blocks or whatever. But, you already have an emulator on your phone running Super Mario... So you will likely skip straight past it.
If you want to help Android catch up with iOS for games, support developers. The next time you look at something and say "oh but it's not free", take a look at that $1 price tag and think about how you're looking at a fully interactive video game which costs you the price of a can of soda. Consider that it might be easier to spend $1 than to seek out a cracked copy, and remember that if the developer makes money, their other games will come your way as well.