Why the title 'Mothers of the Believers' for the wives of the Prophet SAW

I want to understand the reason for the above title . Was the above title given only because they couldn't marry anyone after the Prophet SAW's death (as the Shiites claim with reference as a Hadith from Aisha may Allah be pleased with her) or also out of honour and respect? The Shiites also claim that the title is only with respect to men and not women. Is this correct opinion? For this they quote as evidence the hadith from Aisha R : Narrated from Yahya from Sufyan Al-Thawri, from Firas, from Al-Sha'abi, from Masrooq from A'isha that a woman said: "O Mother." A'isha replied, "I'm not your mother but rather the mother of your men." Source: Tafsir Qur'aan Al-Aziz Zaminain. Vol. 3, Pg. # 387 - 388. And there are more sources here