I recall @GnatGoSplat commenting that on the specific mirrors from the Intrigue, the constant power for the map lights kept the VFD grid powered on, and visible in the dark, and that it was the cause of the drain when running without a BCM. I also seem to recall there being a fix where the grid was either disconnected, or possibly rewired internally to run off the switched power feed instead.
If I had to guess, the constant power actually powers the entire mirror, with the switched powers used moreso as controls to turn on and off the courtesy lights and the mirror/compass. If the grid on the compass display was the main draw on the intrigue mirror, the lack of it on the Sebring mirror might mean there is much less of a draw, even if the circuitry is otherwise identical.