I'm in the military stationed in Hawaii for the whole of 2015 but a California resident. Why do I have a tax due to CA when I did not earn any income from the state?

When you are in the military, generally wherever you are a resident is the state that will tax your income.  

There are some states that allow for an exception to taxation of military personnel.  However, California is not one of these.  If you are a resident of California and stationed elsewhere, California will unfortunately still tax your military income.

For more information on military state residency, please see below: 

https://ttlc.intuit.com/replies/3302301