[throwawayiionqz]

The US has some reciprocity in terms of information flow in the original FATCA agreement. The US (and US banks) does not comply.

Many countries would need information flow about their former or current tax residents to enforce tax obligations, similar to the information the EU banks report to the IRS about US persons. E.g. several EU countries have an exit tax on worldwide income and they would need the reporting from US banks to enforce it.

At the point this is also a competitivity issue for the EU to attract talent and capital. Coming to the EU after having been a US person (citizen or green card) is such a hassle for banking and to manage stock investments in the $100,000s. Just so much pain in terms of paperwork and tax uncertainty that staying in the US and not coming back to the EU solves a lot of hassle.