Earlier quoted context omitted.
Because you're monitoring someone constantly. Imagine if your manager sat behind you breathing on your neck while you coded. He has a pack of tic-tacs so his breath is fine. He crushes the tic tacs with his teeth everytime he thinks you're not working
So many, many workers are monitored by human supervisors already. Not shown to be significantly different.
On the flip side, these bands can monitor every worker every minute of the day. And even the top 10% of workers are likely to receive reprimands for having a bad day, be it a sore knee or being distracted because their children are acting oddly. There's no judgment involved when its automated like this - just numbers that have to be kept above a certain line.