There are two reasons:1. Macquarie underwrote the deal. With...

There are two reasons:

1. Macquarie underwrote the deal. With Deutsche Bank they are obliged to step in an meet any shortfall of the unit holders. When unitholders can't pay, Macquarie and Deutsche have to step in and pay for them. One thing that the current court case should clarify is if they still have to pay up if the company is wound up, and;

2. On top of their underwriting agreement, Macquarie stand to lose another $322 million if BrisConnections is wound up:

http://business.theage.com.au/business/macquarie-threatens-legal-action-to-stop-bolton-20090324-98z4.html

That is why Macquarie are taking legal action to try to save BrisCOnnections.