It’s not a compelling reason; I think it is just a style to be shaven. I bet that the driving reason for this style is porn. Porn is sort of unregulated by real people; normal people don’t admit they have any interest in it, so styles go to extremes so the producers make money. And I think completely shaved is popular in porn cuz it’s more graphic.
Here’s a silly little survey from Huffpost that says shaven isn’t 100% preferred by us ‘normal’ guys.