Everything, because here we're talking about making money with an app. Android share is bigger, amount of downloads is higher, yet iOS apps make
85% more money.
With free-to-play games it's even worse, because the whole point of a f2p game is to incline user to compulsive in-app purchases, and it doesn't work with average Android user. When developers bother to make an Android version of their game, they do it solely to increase coverage, to make more people talk about it, not expecting any serious revenue from that market.