Reduced foot traffic is one of the reasons folks go to the upper deck, among many others.
Not sure why somebody who wants to see the cabin has to walk up and down. It's so small, one could easily come up the stairs and stand at the back with the cabin crew member and have a very nice look without creating footfall traffic by those who might be sleeping or resting.
It's just a technicality, but I thought the reason non-upper deck pax were not allowed to visit was because that is where the access to the cockpit is. And somebody who wants to "visit" and on that visit seems to want to walk toward the cockpit might be one of the reason it's discouraged in the first place!
Even cabin crew in my experience try to limit their own foot traffic during rest times (like the overnight flights).