It’s no secret that app developers prefer iOS over Android. Despite Android having a massive international advantage in market share, many apps continue to be released for iOS before Android and other operating systems.

Thanks to data collected by Business Insider, we now officially know why developers prefer iOS over Android. And to the surprise of very few people, the answer comes down to money.

Business Insider’s research created the following chart:

What does that all mean? In simple terms, it means that for every $1 earned by an iOS app in download revenue, an Android app earns just $0.19. That’s a massive difference.

The difference is slightly smaller when comparing in-app purchases and up-front purchases, but there’s still a sizable gap in every category. For in-app purchases, for example, Android apps earn just $0.24 for every $1 earned by an iOS app.

Essentially, Android is winning the market share battle but Apple is winning the battle for user engagement. Apple users use their devices more than Android users.

This isn’t the first study on the difference between Android and iOS user spending habits. Chikita, an online advertising company, revealed earlier this year that 7 out of 8 internet-connected devices were iPads. Meanwhile, the iTunes store accounts for 67% of digital TV show sales and 65% of digital movie sales.

For whatever reason, iOS users like to spend more money on their mobile devices than Android users. And until that changes, Android users aren’t going to see many Android-only exclusives or Android-first releases.