From United Airlines:
Starting this April, we’re rolling out our new personal device entertainment system onboard select aircraft. With this new service, sponsored by the MileagePlus® Explorer Card, you can choose from over 150 movies and nearly 200 TV shows and watch them free of charge on your personal device.
And from the instructions:
Download the latest United app from the iTunes® App Store if you’ll be using a mobile device. Laptops do not require the app. (Android™ and other mobile devices are not fully supported at this time.)
The process of developing and iOS app is significantly different than developing for Android. Given the small number of iOS devices that need to be tested vs the huge number of potential Android devices and manufacturers, not to mention the fragmentation in supported versions of Android (with manufacturers forking their own custom versions), iOS first is a pretty common theme.