Fortunately/unfortunately, "looking cool", or being considered competent is better judged by what we do, rather than how we look while we're doing it, but the practical and actual REALITY is that the conversion to black trousers, from white knickers, makes it more difficult vizually to pick up officials on the field, especially along the sidelines, in front of the team box areas.
Surprisingly, the wider stripes, make a noticeable difference in the ability of clock operators to spot field officials, and there doesn't seem to vary much interest in reverting back to white knickers.