This is a "have your cake and eat it" problem.

You can make devices around being unbreachable and self-attesting. Go build a SBC and sink in a block of epoxy.

But they also want the appeal of the open, hackable world-- cheap kit that's advancing quickly, commodity technology and infrastructure.

I am actually sort of disappointed we never ended up with a world of special-purpose sealed devices-- put a proper payment terminal on everyone's desk instead of trusting nobody slapped a keylogger into your browser while you're typing card numbers, for example.