Winarta suspects many lawyers believe they are helping law enforcement by informing the public about corruption suspects. Of course, this is a dilemma every law student faces - how to defend a client whom you think is guilty. In my law school days, professors advised simply not asking the client directly about his guilt, and rather focusing on matters that would help in his defense. Also, as Winarta points out, the state appoints lawyers who can focus on proving the defendant's guilt.
However, I'm less convinced this is simply due to lack of education in legal ethics. Given the stigma attached to corruption in modern Indonesia, I wouldn't be surprised if these lawyers might be scared that associating too closely with their defendants might damage their career. Being defense counsel in a tough case is seldom a glorious job, even in the U.S. where being a prosecutor is often seen as more prestigious and a pathway up the legal hierarchy. It might make sense for bar associations to ensure some rotation so that lawyers work on both defense and prosecution. The lawyers I've met who have worked on both sides seem to better appreciate the value of a zealous defense attorney in the pursuit of justice.