No, I get it just fine. What you don't get is you're allowing yourself to be walked all over and letting your manager take the easy way out.
Back when I actually cared about this company, I was at a station up North and would routinely volunteer to go cover a domicile almost 300km away, when someone called in. I'd jump in a van and follow the shuttle up there, help with the sort and then go on my merry way. The one thing I noticed almost immediately is that it seemed like stop counts didn't exist up there. They went out with what they went out with. Domicile employees aren't second class employees and do, in fact have stop counts but what a lot of managers will do is not send up a stop count sheet so most of them don't even know what they're supposed to be going out with.
Most people call in early in the morning, between 7-8. That leaves plenty of time for a manager to come up with a contingency plan but, in the case of you and your co-workers, there is no need for a contingency plan because your manager knows you'll just do it.
As a full-time employee, you cannot be forced to work more than an hour past your scheduled end time but so long as you and your co-workers allow yourselves to be taken advantage of, your manager will continue using your distance to the station as an excuse no to send help. That is what you don't get.