Consider the three modes of being in port: marina, mooring buoy, or at anchor. For two of the three everything - and I mean everything - has to be brought out to the boat by dinghy. And how did the food, water, clean laundry, propane, repair parts, repaired sails, etc. get to the dinghy? Why one lugs them across town to the dinghy dock. Usually for quite a distance. Sure, for a big provisioning run you might hire a cab to take your stuff back. In some ports the grocery store might even deliver. But most days we all (cruisers) buy a couple of shopping bags of "stuff" and lug it back. Even in a marina you still need to get stuff from the marina parking lot to the boat. Assuming you have not already lugged it back from the store. Now most marinas have carts but then you have to load the cart, drag the stuff out to the boat, and then return the cart.
Perhaps all the physical work keeps us young. Touring and swimming are of course also work (as is scraping the bottom.)
I should also mention that like camping rain, bugs, and so forth are a pain in the neck. Oh well.
Fair winds and following seas :)