Every single study done on it shows that creative staff (including engineers) are more productive working where they are less disturbed, that open-plan offices are the least productive environment, etc. So it's utterly unsurprising that people get more productive working from home and can do 8 hour's office work in 5 hours at home.

But even aside from that, if you can complete your work in 6 hours, but can't leave the office for another 2-4 hours because of the office culture, then you'll spend those 2-4 hours doing random stuff in the office. If you're at home, you can leave Slack on and go do something useful. It's not only that WFH gives people more time, it's that it removes the "you must pretend to be busy for 25% of your workday" restriction.

As always, a negative reaction to WFH is a sign of bad management culture. Good managers are happy that their people are getting more done and happier about it. Bad managers see "they're only doing 20 hours a week if they work from home!" and are angry about it.