Cricket will never become clean. Rules are meant to be broken. No matter how strict the rules are, people will find ways to break them. Players come from all sorts of background, have connection with so many different peoples. Unless the players themselves come up front and let the authorities know who they are in contact with, its impossible for anti corruption unit to track the people down.
Indian gambling business is worth over $60 Billion dollar, and from what I read majority of that is under the table illegal gambling. Who knows how much of that money is from cricket, but with all that money floating around, its not too hard to continuously lure players in. I'm sure Sreeshant and his buddies are not the only ones who took part in this sort of activities, they just happened to get caught while doing it. This won't stop others from doing it. They will just be more careful about covering their tracks in the future.