I second @PandoraBoxx‘s quip.
I can come into my office and work any time day or night, weekends, holidays, whenever. But as a salaried employee, I won’t actually get paid anything additional for it.
Furthermore, a lot of building management will turn off HVAC systems outside of normal business hours. And I can tell you first-hand, it gets HOT on the 13th floor of a building in north Texas in August.
And finally, a lot of IT work for systems maintenance also goes on outside of normal business hours. Major work happens almost every weekend. So, while you can go into the office, it’s not necessarily guaranteed that email, network, file servers, web sites, etc. will actually be available for you to use.