At least in the UK, it’s for two reasons: 1. Many older terminal buildings were designed without any space for exit controls. By the time they realized they wo

At least in the UK, it’s for two reasons: 1. Many older terminal buildings were designed without any space for exit controls. By the time they realized they would need exit controls (relatively recently) they realized they could just slurp the data from the airlines’ systems instead. 2. Immigration is chronically understaffed. The government would need to double the number of employees, which is never going to happen.