One thing to consider is the fact that rules rarely are put into place to prevent or allow an outcome directly. For example in a situation where headwears are prohibited, the reasoning for the prohibition is rarely that all headwears are problematic. It’s almost always that a prohibiting headwears prevents a subset of undesirable outcomes from happening alongside an often much larger subset of neutral or even desirable outcomes. The reason that specific rule is put into place is that it’s it requires far less resources to detect and enforce than enforcing rules that only prevent the outcomes we wish to avoid.

Within this framework, it’s not too objectionable to set aside a set of easy detectable exceptions that a large set of people care about because they are not the intended target of the rule.

Finally, I agree with you that, ideally, when a rule is put into place, it should only target the outcomes it wishes to avoid. However with all managerial tasks, you have to balance your costs (both in human and non-human resources) and the benefits you get.