So he shows up for work and they just don't like the way he looks with short hair. It isn't "alien" enough. So someone (Brad Wright? Jonathon Glassner?) asks him, "What do you think about bald?" and assures him it will only be for 2 or 3 years. So at the beginning of each season Chris would ask about Teal'c getting hair and the producers would veto it.