The foreign banks respond: "Ok, we won't deal with any Americans", which makes life harder for Average Joe Expat
Not exactly. US government wants to repatriate taxes earned by American people and capital abroad and making foreign banks accountable to US is part of making that enforceable.
On-shoring of dollars into US accounts because they can't be kept easily abroad is unpleasant side effect. When US dollars leave US, economically it is the equivalent of the World giving US treasury an interest free loan. The return of those dollars is essentially a repayment of that loan and acts as inflation economically. This could be useful, but the US government already has a direct lever on the quantity of dollars in the US economy through the FED.
To summarize, US Gov only wants the return of dollars that it will receive as taxes, but by all means don't bring back the rest.
Really? The USA is considering everything as under its jurisdiction, but the banks are overreacting?
I would also say that if the IRS is able to enforce their rules without war planes, then it is technically within their jurisdiction. The jurisdiction comes from a) legal jurisdiction within the USA and b) treaties that allow them to enforce laws beyond the USA.