Answer:
One issue is huge, yet almost nobody knows about it. This is changing but ever so slowly.
In 2010 Obama signed a law known as a the HIRE act and contained within that, with almost zero scrutiny, zero debate, no cost/benefit analysis and certainly no consideration of what turns out to be an absolute laundry list of negative consequences for the USA and ultimately the world, is FATCA.
What is it?
It is an attempt by the US treasury to net an alleged 100 billion dollars per year in tax revenue hidden overseas by US citizens, a figure totally discredited. It was spawned by the success the USA had in finding real hidden funds in Swiss banks, but that money is gone.
Having seen the fate of the banks involved, no bank is wilfully assisting American residents to hide funds.