I believe it was to do with MultiDex support, you can have it I think below 5.1 although for the sake of not breaking things before my release I left it at supporting only 5.1 and above! I also think there might have been a plugin that doesn’t support below that, although I can’t remember which one off of the top of my head right now!
I’ve added it to my ever growing list of things to investigate further 
Asterun has been updated! 
This update includes the latest Cocos2d-x version, alongside the introduction of some volume sliders to change the backing and effects volumes! There’s also a few bug fixes, but lets not talk about the bugs
Asterun also includes some of the open-source code I’ve released over the past few weeks: AudioHelper, SimpleSlider and ModalAlert. Feel free to check out the code and give it a test in Asterun! 
Don’t have it yet?! Download Asterun here! onelink.to/asterun 