I think one significant part of the low turnout among US overseas citizens is quite simply the typical voter suppression associated with postal voting in general, including people simply not being told their own rights, exacerbated by some added bureaucracy from being situated outside of the USA and the ballot needing to pass through different postal systems. There might also be some demographics overrepresented among overseas citizens that have their own obstacles to voting, too. This is all a neat explanation of why my own family has generally not voted, however I don't think this is the full story.
Another US overseas citizen on Hexbear remarked when I brought up the low turnout yesterday,
I'm an overseas American and I am not voting because it would be a bizarre waste of time. Not only would I be voting by mail in a solidly blue state but if votes by mail ever determined an election there would be a coup.
Indeed it seems to be in the "battleground states" where postal voting rights are most challenged. So it would seem that the states where it is easier to vote from abroad, are also the states where there's nothing "competitive" about the elections to begin with.
What stood out to me more in that reply, however, was the remark that "there would be a coup" if postal ballots ever determined an election — essentially that the fact that postal ballots are already treated as inherently suspect, would in itself demotivate people from voting in the first place.
Otherwise there are probably many US overseas citizens who think of the elections as fundamentally illegitimate for other reasons, or who see both wings of the Capitalist Party as roughly the same — for better and for worse — and so they just wouldn't bother voting even for a "third" party.
Or there could be other reasons! Like maybe there might be a stigma against voting in US elections from some countries, because this might make the voter look "disloyal" to their new country, I don't know. This is just speculation.
So I'm hoping someone might have more insight into this topic, or might be able to even say the relative prevalence of different reasons why US overseas citizens don't vote.
This also opens up a related discussion about why specifically overseas votes would be suppressed. I mentioned "seeing both wings of the Capitalist Party as roughly the same, for better and for worse" in the post above — and when I say "for better and for worse" there, I am referring to the different types of US overseas citizen.
The main thing that sets US overseas citizens apart from stateside citizens is that US overseas citizens are obviously much more directly impacted by the USA's foreign policy than stateside citizens, however this can be in different ways: some US overseas citizens might personally benefit from the USA's foreign policy, these will generally be US overseas citizens dispatched to actually uphold said foreign policy in one way or another; other US overseas citizens would find the USA's foreign policy very detrimental to themselves, and so they might be more critical of it than many stateside people, for whom the foreign policy serves as the "magic machine behind the curtains" that makes their material comfort possible. Many others would find themselves somewhere in the middle, e.g. if you're in Western/Northern Europe you might benefit from the USA's plundering of the global south, but you might also notice that your own country is a vassal of the USA.
There could also be general paranoia about votes from foreign countries bringing in "foreign ideas" that would destabilize the current system, especially if these are non-core countries or countries outside of the settler-colonial paradigm; or that foreign votes could give those foreign countries an advantage over the USA.
However, in practice I'm pretty sure that most US overseas citizens live in the imperial core, in which case I think that for most of them, the differences they might have from the average stateside eligible voter might not actually be that big. Like I've been critical of the US military presence and US cultural imperialism in Norway for as long as I can remember, but the fact remains that most US overseas citizens in Norway I've interacted with aren't nearly as critical, and even I still naïvely voted Democrat back in 2020.
Which brings me to an idea I have of "splashback": that systems of in this case voter suppression, might be targeted towards one particular marginalized group, but might also end up incidentally impacting a different, largely privileged group — and that "splashback" is allowed to happen so long as it isn't so intense that it actually threatens the whole structure.
This isn't to say that I believe that the suppression of overseas voters is entirely coincidental, just that it might be to some degree intentional and to some degree incidental.