Oh well, i feel like i am repeating myself 
. Yes BBL window is Dec-Jan but they always play international home series at the same time, no matter what, Don't forget about "Boxing Day Test" which is fixed for X-mas.
2016-17 South Africa tour of Australia (Oct-Nov-Dec-Jan)
2017-18 England tour of Australia (Nov-Jan)
2018-19 India tour of Australia (Nov-Jan)
2019-20 NZ tour of Australia (Dec-Jan)
2020-21 Upcoming India tour of Australia ( Nov-Dec-Jan)
. Yes BBL window is Dec-Jan but they always play international home series at the same time, no matter what, Don't forget about "Boxing Day Test" which is fixed for X-mas.2016-17 South Africa tour of Australia (Oct-Nov-Dec-Jan)
2017-18 England tour of Australia (Nov-Jan)
2018-19 India tour of Australia (Nov-Jan)
2019-20 NZ tour of Australia (Dec-Jan)
2020-21 Upcoming India tour of Australia ( Nov-Dec-Jan)
Well.. that's also true. BBL doesn't get the same importance from CA, as the IPL gets from the BCCI. The revenues are not that great, and that may be the reason. As far as I know, CA get a majority of their revenue from bilateral series and other matches involving the national team. The case is different with BCCI and the IPL. But this may be changing. BBL rights got auctioned for a very high amount in 2019.