The prohibition on certain clothing is not due to uniformity or appearance or anything like that. It's due to physics. Certain kit will improve/enhance speed (mostly aerodynamics).
In open time trials for triathlon, sleeveless skin tri suits are often prohibited. Like seriously, they require a certain percentage of the arm to be covered. In other cases, sleeved are banned. (USAT for example)
I have seen people disqualified for this.
Those folks wore the previous year's kit, and were thus disqualified for having sleeves.
For the regulating bodies in question, this isn't a matter of religious accommodation or religious discrimination. This is a result of micro-regulating every aspect of the race to flatten the playing field as much as possible. These race outcomes are measured in and differentiated in microseconds, and the rules are stringent in ways that actually make THIS issue not even the most contentious issue to consider.
Without considerable wind tunnel and other testing, they are right to ban it on potentially performance-enhancing grounds. There are SHOES that are banned for form/function.
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