How do these phone charging stations work? I saw a newsstand offering the service recently.
Back to the OP - the reason is that it's not practical. It's great for them to have a selection to loan you if you forget yours, but having a dozen different chargers hanging around in every hotel room just isn't going to work. Even if hotel did advertise such a service I'd feel the need to bring my own charger anyway just in case theirs didn't work or they didn't have the right one for my phone. That's too big of a risk.
If only there were some kind of universal standard for this stuff