Perhaps because the other dress code constraints are for more universally accepted reasons while the question of things like the hijab/niqab are tied to an inherent contradiction within one of the standard political camps, disrupting the placement of the (un)acceptability line. Wearing a uniform is a sign of responsibility. (If you wear the fuel station attendednts’ uniform, you are responsible for the fuel station, etc.) Wearing a minimum quality of clothing is related to the service provided. (Showing up to a black tie restaurant in board shorts and flip flops ‘lowers the tone’ of the restaurant, which is often more the product being sold than the actual food. In that kind of restaurant, you are paying more for the exclusivity of the space than the chef’s produce.) However, Muslim women’s headjoys are more fraught because they simultaneously occupy two symbolic spaces, one as a symbol of Islam itself, which is coded as evil by one broad sector of politics and, because of that, something to be protected by the opposition, but the other as a symbol of Muslim patriarchy, which has the exact opposite coding by the standard broad political binary. Resolving the hypocrisy would require abandoning one set of symbols or the other and taking a position currently held by the opposition. Most people aren’t willing to do that.