By checking for fealty to the false “stolen” narrative at the outset, Trump’s allies aren’t simply weeding out people who disagree, they’re weeding out people who won’t acquiesce to the Trumpian approach to reality. They’re not just getting rid of people who won’t go along on this one subject; they’re getting rid of people who won’t go along in general.
This might be why Amendment 14 Section 3 was supposed to be self-executing. But I’m not American so what do I know?