It's not just photo. It's as simple as people just wanting to be able to do things intuitively and easily. Hey I took a great photo at the weekend, let me share it with you, here you go, done. Or you must hear this song, or read this etc. Sharing has to be very easy.
I have an Aunt with an iPad full of photos, that she's pretty clueless as to how to backup or share. She's given up trying and just takes her iPad to her friends.
I have another Aunt who can't for the life her, get photos from her camera to her laptop. It's a trial.
So if you have a phone with a camera, that lets you seamlessly share photos, even if it's through imgur, facebook, or whatever, it's probably going to be easier than connecting up cables, trying to traverse file systems etc.
My brother wanted to sell a motorbike, and wanted to send the buyer a couple of photos. He was absolutely dumbfounded by the process because his SLR took big photos that his email provider rejected. He's not that web savvy. In the end I said it might be easier for you to just install Dropbox, and it was. How arse about face is that?
Even copying files onto some people's computers doesn't help that much, if their file management skills don't exist.
OSs (desktop) haven't functionally changed that much in the last decade on the face of it. And even the simple problems haven't been solved, which is laughable when you have an insight into the complexity of some of the work arounds.