It's just the way things have always been done here. Things change very very very slowly here. Your recurrent checkrides are also every 6 months. One way to look at this job is to take it 6 months at a time. Some look at it like a daily job. One bad day ie a hard landing or other Level 3 QAR and you are out. I tend to take it 6 months at a time but don't come here thinking its a 20 year career. Most guys last 1 contract.