I'm not sure I follow. I am a US citizen and have never lived abroad, but my understanding is that US Citizens living abroad must still pay the US a full federal income tax. It's graduated/progressive, of course, so the actual percentage may vary, but it should probably be between 15% and 40% of income. Not what I would call small. I don't think they can deduct local taxes, can they?
There's a huge exclusion.
The 2026 Foreign Earned Income Exclusion (FEIE) allows qualifying U.S. expats to exclude up to $132,900 of foreign-earned income from their U.S. federal income taxes. Married couples can exclude up to $265,800 if both spouses work abroad and each meets the eligibility requirements.
Many countries have tax treaties with the US, and there’s also the Foreign Earned Income Exclusion (FEIE), which excludes up to 132.9k of foreign income; so many US citizens abroad will indeed pay no US income taxes.