in fact, having one may hinder a brother from bringing glory to God by his dress and grooming and his being irreprehensible
JW's decided long ago that dressing in the style of "Corporate America" fit into their idea of acceptable even though they view Corporate America as corrupt and say it's wrong to emulate the worlds standards of dress and grooming.
There are people who highly distrust anyone wearing a suit and tie because of their past dealings with those in positions of power whether they are Buisiness Men, Politicians or Religious Leaders. Often, such as in court, someone who is trying to appear more respectable than he really is, will put on a suit and time.
For some people, there may be less hindrance to the Glory of God if his message came to them from someone wearing a beard and casual clothing. For others, just knocking on their door like an annoying salesman is a hindrance to the message of God as well yet no one suggests dropping the door to door work lest it turn anyone away from the message.
In this matter of Beards, there is more going on than beards being a hindrance to the message. I suspect that, someone in authority back in the day, wanted themselves apart from C.T. Russell supporters or perhaps they didn't like them or couldn't grow one themselves. As is so often is the case, they found a way to make man made notions appear as if they were about concern for Gods will.
In the early days of Disneyland, Walt Disney banned his employees from wearing beards and moustaches because in his growing up years, he associated them with "Carnival Barkers" and the Villains in his stories always had moustaches or beards. He wanted to set his theme park apart from trashy carnivals and wanted his employees to look like the good guys in his stories. But at least he owned up to it and didn't try to insinuate that it was about God.