I was under the impression that these automated systems had "reduce personnel" as their primary goal, more than speed.

This would explain why the bad, but still automated, scanning stations still exist.

I've always seen a bagging area just after the scanning station here. I'm not sure it's the same in Japan. But all the people I've seen start to bag while the items are scanned. This results in the cashier waiting for you to pay, blocking people in the line.

With the systems I've discussed in the beginning, you basically bag your items as you go. In the normal case of no-recheck, you pay and leave.