I'm no EE, but my understanding is that it's partially because the amperage is very low and partially because the signal is AC operating at a frequency that cau

I'm no EE, but my understanding is that it's partially because the amperage is very low and partially because the signal is AC operating at a frequency that causes a large impedance mismatch between the probe and people. It's counterintuitive enough that the probes actually have an "anti-warning" label to inform people that they are safe to touch.