Why were men separated from women in the place of ablution, even though that was permissible during the time of the Messenger of Allah, may Allah's prayers and peace be upon him?

The scholars differed regarding the meaning of the hadith of Ibn Umar, may Allah be pleased with them both: "Men and women used to perform ablution together during the time of the Messenger of Allah, peace and blessings be upon him." Some said that they would perform ablution in one place but each separately, while others said that the men would perform ablution, and then the women would follow them. Al-Hafiz Ibn Hajar preferred the view that mixing was permissible before the revelation of the verses of hijab, and thereafter it became restricted to wives and mahrams. Based on this, the separation between men and women occurred during the time of the Prophet, peace and blessings be upon him, after the revelation of the verses of hijab, and there was no mixing during the time of the Rightly Guided Caliphs.