He didn't do much litigation. He represented MALDEF, and an individual named Calvin Roberson in a redlining case. He only ever had 30 clients all told, and he contributed to most of those cases as a writer or researcher. Obama worked for about 10 hours on Rezko's various projects while Obama was at Miner Barnhill & Galland.
A junior associate at a law firm takes the cases that he's given. Rezko at that time was no different from any of Miner's other real estate clients, I imagine. Obama only worked 3 years at Miner, and in that time he made a small handful of court appearances. This is normal, if you know jack squat about how the legal business works.
I think you'll find that ANY Harvard Law graduate, and in particular the president of the Law Review, can pretty much get any job he wants. The fact that Obama chose to work for a firm that had a rep for doing civili rights litigation says a lot about his character. He could have easily taken some high-paying job in a corporate firm in New York, but he chose not to.