More than this it's just a good way to build regular hand washing into a routine. You already use a restroom a few times a day at fairly regular intervals, so you only have a few hours worth of microbes on your hands at a time.
Honestly, this feels like a meme. I have been eating man ass for years and I am yet to find someone with an unwashed butthole. Considering how often I see this claim, one would think it would be a more common problem.
Not saying it can't happen but, Do you have any first hand experience to support the "So many men don't" part?