Justice Nye Perram was forced to agree with DBC LLC over the matter of copyright infringement, so they won on that case. However the Justice was also aware of what happened in the US when the studio's lawyers were permitted to go on a fishing expedition through the ISP's customer records then send them what amounted to extortion notices threatening an expensive law suit if they didn't immediately pay a sum of money. So called "speculative invoicing".
To prevent this, the justice made DBC LLC pay a bond of about A$600,000 which would be forfeited if they tried speculative invoicing. The agreement meant any communications with the ISP's customers had to be vetted by the courts. After having repeated attempts rejected because they asked for far too much info and were pretty much a prelude to speculative invoicing it became clear to DBC LLC that they would never make a profit on this and simply cut their losses.
I think I'm pretty safe in saying that the reason DBC LLC has withdrawn their case is just to get their bond back. Dallas Buyers Club was technically in the right, but did everything in the wrong way. That being said, I doubt the Justice was ever going to let them profit on it, setting a precident that you shouldn't go after end users in Australia, even if you are technically right.