Because forbidding women from wearing particular things increases their freedom. And making them feel that they can’t leave the house makes them more equal. And there’s nothing Islamophobic about this. After all, a Christian who wanted to cover their face would also be prevented.
Please don’t misunderstand me: there is plenty to criticise about the views underlying a demand for women, but not men, to cover their faces. But there’s also plenty to criticise about e.g. traditional marriage vows (“obey”), and I don’t think they should be banned either. (Though I do think one could make a better case for banning those vows than for banning niqabs, now that I reflect on it.)