I think I’d better begin my reply with a disclaimer… Insofar as everything you’ve written applies to you (ninthace!), there’s absolutely no reason why I should think it applies to me or to anyone else. So what follows is purely my reaction to the advantages you see in shorter walks. Oh, and I note that you define your ‘shorter walks’ by duration, not distance. I typically walk between 8 and 13 miles during your times, and I would call those distances short-to-medium.
So, to each of your points in turn:
I enjoy walking whatever the conditions and I’ve never cut a walk short or not gone out at all because of the weather. I especially enjoy walking in the rain for several reasons: I get to wear some gear I rarely use (such as my waterproof trousers), there’s usually hardly anyone around, and I like splashing through puddles. In fact, during the lockdown period, the only outdoor walks I did were when it rained – just twice, as I recall!
I walk for both health and fitness benefits and the fitness benefit I find most beneficial is endurance. If I limited all my walks to a couple of hours, then I doubt very much that I’d find an occasional 50km particularly straightforward. In my experience, fitness trainers say that the real gains are made when you go beyond your comfort zone. I don’t tend to push myself any harder on shorter walks than on long ones. If anything, my shorter walks are more likely to be done with family members while I often do solo long walks against the clock.
A walk of pretty much any length can serve as reconnaissance. I find that the longer the walk and the further from home I am, the more likely I am to spot promising paths to explore another day.
My backpack and its contents aren’t really an issue for me. I always carry drink and snacks, appropriate clothing (I hope!), and all those little extras such as compass, first aid kit… and now sanitiser and facemask as well. In fact, if I do a short walk of any kind without a backpack, it feels strange.
I really can’t relate to the final point. I believe I’ve walked almost every footpath, bridleway, byway and road within a 10 mile radius of where I live, so there’s nowhere local left to discover. While in my (slightly postponed) quest to completely cover Kent, I drive ever further to explore new areas and so I usually plan walks of between about 15 and 20 miles to make the drive worthwhile.