Why minSdkVersion is 21?

[emanuelb]

The minSdkVersion is 21, so the app won't work on android version < 5.
There was people complaining on the app won't work on older devices (heard at news), what the reason it's set for 21?
From react-native documentation:
https://github.com/facebook/react-native#-requirements

React Native apps may target iOS 10.0 and Android 4.1 (API 16) or newer.

Which component / tasks require the increased minSdkVersion?

See #281 (comment) for news mention:
"היישומון אינו נתמך במכשירים ישנים"