amorphose: They filed the lawsuit on July 31st so it hasn't been that long. They attempted to negotiate with SM privately several times but SM pretty much ignored them, thus this lawsuit was filed and everything blew up from there.
My guess on why they waited until now to speak up is because they have a very large impact in the industry atm, especially now that they have great success in Japan to back them up. They actually stand a chance against SM now. If it was some newbie group, they would have just get tossed aside for newer talents, unfortunately. This case got huge coverage not because it's artists vs management but because it's DBSK vs SM.
Cut from History in Japan 4