It's not. The iconography style stems from the Papist persecution of the Orthodox Christians of Transylvania in the late 17th century, and throughout the period where the Habsburgs controlled the region. They destroyed Orthodox churches, overtook the ones they didn't destroy and forcibly converted them to Uniatism. Priests would teach laypeople how to write their own primitive icons on glass so they could continue to worship in secret. Look up the history of the Nicula icon and the Nicula monastery.