Payne conceded that "the use of biometrics to open an electronic device is akin to providing a physical key to a safe" but argued it is still a testimonial act because it "simultaneously confirm[s] ownership and authentication of its contents," the court said. "However, Payne was never compelled to acknowledge the existence of any incriminating information. He merely had to provide access to a source of potential information."
If you can be compelled to hand over a key to a safe, I can see how that translates to putting your thumb on the scanner.
The constitution is only used to protect property rights of the owners and the power of managers. The working class is not often afforded it's protections.