Maybe the Vulcans somewhere along the line decided that shaving is logical.
They have their own cultural norms just like any other species... so it wouldn't be that out of place (considering they also practice relatively 'barbaric' rituals to resolve Ponn Far).
At any rate, Vulcan logic has its quirks... and humans have challenged them on occasion.
Which would help explain why Sybok grew one. He eschewed logic so he embraced the symbols of his people's ancestors. Facial hair being one.