Data security?
I pointed out that the Canadian owned (at the time) NextGen were in the picture in a response to this post:
http://www.theregister.co.uk/2016/08/07/it_analyst_oz_census_data_processed_as_plain_text/
The SSL/TLS connections terminated on their network. They potentially had access to all the responses on their network.
So we have at least two foreign powers having access to the data submitted online.