Well, that's the other side of it. If a company is paying you for 40hrs a week, they want to make sure they're getting their moneys worth.

Of course you can argue about how employees, despite being "in the office" are only productive for 2 or maybe 3 hours of their 8 hour shifts. But that's now how management sees it. Having a person visibly in a chair makes management feel like they are getting their money's worth.

I also don't get how people expect to get paid a full living salary for working less.