Because companies assume if you've got time to dick around after your work is done then you've got time to do more work till your 8 hours are up. At least that

Because companies assume if you've got time to dick around after your work is done then you've got time to do more work till your 8 hours are up. At least that's how it's where I live in Europe. Companies feel entitled to the full 8h per day of productivity so if you know everything out in less then that they want to see it and give you more work to fill the remaining time, which Is why WFH is very rare and in office work is the norm here (Austria).