>One answer is that the only reason they can get away with citizens is that they are a captive audience.

In addition to this, there's little citizens abroad can do to affect change in the US. Sure, we can vote; your "residence" for voting purposes is presumed to be where you last lived in the US. But say I write my Congressman about an issue that matters to me as one of his constituents who lives abroad? I'd probably safely guess I'm the only person who'd have done so within his district. I'd guess there are dozens of people in my situation in his district.

From across the US, there are estimated to be 3 to 6 million non-military American citizens living abroad. That's more than a number of states. Yet any hope of responsive representation is a fantasy.

Part of the hardship of deciding to live abroad, I suppose.

edit: State Dept. estimated 9 million abroad in 2016.