Jilbab As Temporary Protection
السلام عليكم According to Ibn Ashur, one of the great exegetes of the Quran, the free women used to wear this cloth in the day, but did not wear it at night when they went for the call of nature. This was a sign of free women. Now, because of their not wearing this cloth at night, the hypocrites were able to make excuses to harass them, saying we thought she was a slave-girl. So, Allah ordered women to wear this cloth at night time too so they can be distinguished from the slave-girls and not harassed. Feel free to correct me if I didn’t present the view of Ibn Ashur correctly. Regarding your second question on whether all of the free women used to wear this cloth or not: I don’t know.
The injunctions of wearing jalbab doesn’t not mean that that did not take it and now they would start wearing it. It means that this practice was declared to end the excuse of the culprits. We find in Quran the injunctions not to marry your mothers sister etc it doesn’t mean that they were prohibited from a thing they were doing. This is the statement of a law. Here too this practice of theirs was made a law to end the excuse and give govt a right after this warning that they would start operation against them.