Additionally, in order to save the images I want how I created them, I'd have to pay a non-insubstantial amount of money to store them. By saving everything locally, I can have the full-resolution image for my own usage, and just pay the occasional cost to upgrade/replace hard drives.
Furthermore, I'm almost certainly going to have to have a copy of many of the images on my computer anyways. A lot of the images I make, I tend to want to share in 2 or more other places, not just a random web album. So again, the webapp usage story falls apart.
I'm also not always in a place where I have internet access which is particularly fast and reliable. So, needing a webapp in such a situation means that I can't edit and arrange my photos at all until I get to a location that has internet access. Not everyone wants to be hyperconnected all the time.
Webapps mean you're even more beholden to someone else for functionality than a desktop app. You are limited in how you can post your content, where you can post your content, and even what content you're allowed to post. A desktop application has none of these limitations, whereas they're inherent flaws in the webapp ecosystem.