I would think for two reasons:
If they had come out and said the truth probably wouldn't have swayed a judge one way or another, since he is there to rule on the matter and not on possible consequences that may result from that verdict. In other words, their unfortunate (financial) situation isn't of any relevance. The second reason is probably of embarassing nature, of not wanting to admit to the "mess" they created with the contracts, so they were effectively trying to get out with all the other arguments on the basis of safety etc.
I would have thought that to some degree, Sauber could argue that "events" and "circumstance" of higher power forced them to breach the contract with VdG (it did, because the original plan was to race VdG alongside Bianchi which would have given them money + an engine deal with Ferrari - then Bianchi crashes and the engine deal evaporates and Nasr and Ericsson become available). The problem is - that is probably what they should have argued (maybe they did?) in Geneva in front of the Swiss arbitration court. As far as I understand, all what the Australian Court is doing is determing that the verdict in Switzerland is valid and can and should be enforced in Australia and its Grand Prix. That the Swiss arbitration ruling isn't 'final' or legally binding yet is probably irrelevant (Sauber, AFAIK, has appealed that verdict, but no idea when that will proceed?).
Anyway, I'm utterly stunned that a court can force the team to run a particular driver. While a pay-driver contract is probably a lot more complex than simply a contract between an employer and an employee, the matter of the fact still remains that no driver can ever be bigger than the team. And if the team in question (Sauber in this case) despite all financial payments by their pay-driver wish to terminate that contract, the only thing a court could force them is to pay out compensation and damages in a determined fashion. If the team then goes into administration as a result of them not being able to meet those (and other) payments, so be it. But to force them to run that driver? That IMO is dangerous territory, not only for Sauber, but technically for any team that employes a pay-driver (or any driver who I guess has some entitlement to the seat he signed) and is for one or another reason suspended.
There is the argument of course that a F1 seat is something special, an event and that there is a higher meaning to being able to race or participate vs. something a simple compensation could manage, but in terms of F1, it is not only a drivers sport - it's a team sport too. The driver are but two individuals inside an organisation with hundreds of employees (in the case of Sauber ~300)...
At this point, I'm actually seeing Monisha praying that that superlicence doesn't arrive in time...
(I'm not against VdG per say, but as a Swiss, I am very concerned about Saubers situation as a race team looking forward...)