Just because you are at the office, doesn't mean you are actually working. Just like me sitting at my desk at home isn't actually working.

The difference is that in the office people pretend to be working.

But if you're there, you're working. You can't spend that time out at a stadium watching a ballgame, or hiking through a forest, or catching up with old friends over coffee, or fixing that stubborn door on your house, or with your family. You're at work, in work mode and your time and energy are alloted to that.

If you work for an agency, and sales is having a tough time closing a deal so there's no work for you today, but you have to be there anyway, ready to work or finding other things to do, maybe upgrading your tools, practicing/learning, then that's still work time. It's not leisure time.

Just because you don't achieve 100% uptime cranking out widgets non-stop at full productivity doesn't mean you're not working. We're people, not industrial factory machines.

You can say 'people are pretending' or 'that's not actually work', but it is. And saying that it's not is just denying reality by casting a moral judgment on it like that.

In the context of of this post I see working as the equivalent of being productive.

I agree with you that sitting at my desk or being in the office is work time regardless of what I am doing and therefore should also be paid.