(Note: nothing in this message should be construed as support for the US thinking that non-US accounts or non-US income of US citizens should be any of their business.)
There's a large difference between backdooring end-to-end encryption and accessing financial records that are already by design available to the financial institution.
Why would the IRS need to access my records? Or need to impose non-US citizens to sign affidavits outside the US?
FYI I am not a "US Person", whatever that means, yet when I signed up with my bank account in an EU country I had to sign an affidavit claiming I am not a "US Person", although that designation has no meaning in the local laws.
(Note: this is an explanation, not an endorsement or any form of support.)
These requirements are in place in part because the US wants to tax the income of US citizens no matter where they are in the world. So, they make requirements like FATCA and make requirements on foreign banks that amount to "we won't do business with you unless you impose these requirements on all US citizens (which inherently also means asking everyone if they're a US citizen)".
These decryption requirements are being put in place in part because the UK wants to find potential criminals no matter where they operate from in the world. So, they make requirements like back doors and make requirements on companies that amount to "we will fine you a % of your global revenue unless you impose these requirements on all potential criminals" (which inherently also means decrypting everyone's messages)".
