They really should, that way everyone is competing on equal levels. Less variables means a greater chance the best person wins.
Or it would benefit those participants who are best suited to the chosen gear.
Taking an extreme example - imagine if we said “everyone must wear size 9 shoes so everybody’s on equal footing”.
For example, road bikes have different frame shapes that are suitable depending on your torso length compared to leg length.
Of course, the natural next step would be allow some flexibility (different frame size but same material), but you can see how that could be a slippery slope of legislation and lobbying that would end up in a similar situation to where we are today?