Because it’s not about supporting QF/VA. The entire point of IFAM is to get the exports to their destination. Without Singair/EK/Qatar/Etc feeding freight from Australian destinations into their wider network, those exports would rot in Australia.
Whether QF or VA should be receiving the money, is entirely missing the point. VA only flew to LAX. QF also had a relatively limited international network within Asia (compared to big freight carriers). As other posters have mentioned, cargo has not been a big part of Aus airline ops.
Sometimes it’s about more than just “support Aussie airlines”.