Maybe this has something to do with it.

In accordance with the FIFA Regulations on the Status and Transfer of Players (RSTP) and the FFA
National Registration Regulations (NRRs), any player who has a written agreement with a club and
is paid more than the expenses they incur in playing for the club must be registered as a professional
and not an amateur. If an amateur is paid or reimbursed more than $110 per week, the onus is on
the club to satisfy the competition administrator that the amount accurately reflects the expenses
incurred by the player (see article 3.1(c) of the NRRs).
Other than for National Leagues Competitions (A-League, W-League and Y-League), the contract
between the club and the professional player must be in the form of FFA prescribed form NRR05
(see article 6.1 of the NRRs) and lodged with the relevant competition administrator during a
registration period (see article 4.4).
It is the club’s responsibility to ensure that a player’s status as a professional is accurately recorded
on the Play Football registration system at all times (see article 3.1(d) of the NRRs)