First. Bug Fixing is not as simple as just pressing a Button or set a Value from 1 to 0. Some Bugs can be very complicated and nearly impossible to find in the Code, despite being right there ingame.
Second: There are many Bugs that don’t exist until the Game goes live or certain Patches hit on Tuesdays. It may sound odd but Software can react different to Live Envirnment than it reacted on Test Environment.
Third: Fixing ALL Bugs is just unrealistic, every Program will have Bugs.