Well, all humans have the instinctual impression that facial and body hair is more masculine, so the more beard, the more manly. Growing a thick, lush beard, and maintaining it well, give the impression of good health, which indicates security and good genes for starting a family.

There’s also the societal image of the “lumberjack” type, inspiring associations with strength, work with their hands and arms, and being a rugged protector.