U.S. tax law is the first and biggest barrier. It is unlikely that U.S. expats in France would face U.S. taxation in practice, and when it is owed, the tax burden is likely to be very modest. 

[Earned income of expats up to a substantial threshold is exempt from U.S. income taxation][1] ([$104,100 USD in 2018][2]), and the foreign tax credit reduces any U.S. tax that is due by any tax paid abroad to a foreign government.

In general, the higher income and passive income taxpayers who are potentially subject to U.S. taxation, since their income isn't entirely excluded from U.S. income taxation, pay higher tax rates in France than they do in the U.S. So, no net U.S. tax is due. The tax rate on a typical high income earner in France is [58.1%][3], which is typically more than enough to eliminate U.S. federal income taxation (with a [top tax bracket of 37% in 2018][4]) through the foreign tax credit (and of course, expats are not subject to U.S. state and local taxation because they don't reside in any U.S. state or locality).

There could be a U.S. estate tax burden could be a form of double taxation, but that only impacts U.S. citizens with more than $11,180,000 USD individually or married couples with more than $22,360,000 USD. No doubt there are a few dual French-US citizens who have to worry about that, but not many.

  [1]: https://www.irs.gov/individuals/international-taxpayers/foreign-earned-income-exclusion
  [2]: http://premieroffshore.com/foreign-earned-income-exclusion-2018/
  [3]: https://www.bbc.com/news/magazine-26327114
  [4]: https://www.nerdwallet.com/blog/taxes/federal-income-tax-brackets/