ADE requires devices to be assigned to an MDM server in ABM. The Apple Business Manager User Guide states, "For devices to automatically enroll via ADE, they must be assigned to an MDM server in Apple Business Manager. Without this assignment, the enrollment process will not initiate during setup." Options A, B, and D don't apply as devices from Apple are auto-added, don't need resets, and location issues don't block enrollment without assignment.
Reference:
Apple Business Manager User Guide, "Assign Devices to MDM" section.
Apple Platform Deployment Guide, "Automated Device Enrollment" section.