Because virtually all construction companies in the UK require their workers to have a CSCS card and you cannot obtain that without first passing the CITB HS&E test. Construction companies have a vested interest in ensuring their workers are properly trained in the latest safety and health practices. This enables them to avoid careless accidents that can cause expensive delays, property loss, or worse, injuries. CITB HS&E certification enables them to rest easy knowing the worker does not represent an unnecessary hazard.