Why is Axl private at the moment?

The answer is actually pretty easy, Axl is currently still being worked on a lot.
Functionality is being added or removed.  
Some stuff gets total overhauls.
Overall, the bot is still not finished nor in a state where i personally would say "This is ready for being pushed out"

When will Axl become public?

That is a very good question actually.
I dont want to set a fix timeframe, as working on the bot is a lot of work, aswell as studying and moderating GAM.
The bot will become public once it reached a state where i personally feel "safe" when publishing it.