Originally Posted by
nzkarit
Because it is faster and simpler to present your passport to the kiosk, than having to mess around in lounge or gate verifying your passport
Yip exactly this. It actually is a PITA for ground staff to manually verify passports and takes 90 seconds to use the kiosk.
Check-in doesn't close at T-60, it's closer to T-45 but can vary.