Indonesian is a high risk county from where some people try to make an unlawful entry into Australia.
While AU has for some TWVO (Transit without visa as link above) and for other passport holders a transit visa (even if airside), the airline is taking the risk
If the OP had a VA ticket DPD-SYD and a separate VA ticket SYD-ZQN (Queenstown, NZ) the response at DPS check-in may have been different [no idea if VA schedule allows that same day. A cheapie ticket AU - NZ may not have convince the airline.

Clicking on the airports TWOV is very limited due to AU airport operation. VA DPS were being conservative
AU Govt -->Transit facilities at Australian airports