Why is "peace be upon them" not said for Abu Bakr and Umar - may Allah be pleased with them - even though it is permissible for Mary - peace be upon her - and they are better than her?

It is disliked to utter the phrase "ʿalayhi al-salām" (peace be upon him) for anyone other than the prophets. Although Mary is not a prophetess, the custom of scholars has been to say "ʿalayhā al-salām" (peace be upon her) for her, especially since the Quran alluded to her unique status by her and her son's safety from Satan. This supplication is not used for the Companions; instead, "raḍiya Allāhu ʿanhu" (may Allah be pleased with him) is said. This does not mean that Mary is superior to Abu Bakr and Umar, for they are the best of the Ummah after the prophets.