Primarily because the biometric technology is poor, and there is still an unacceptable level of error. Even INS are having second thoughts about expanding the INSPASS program.

These two sites are continuing in the pilot project. If they can improve the reliability of the hand geometry reading, then further expansion might be an option.

Flavour-of-the-month is retinal scanning, but there are some concerns about the travelling public's comfort level with that.