a) These days people need validation in order to value an experience. I think it might come from the fact that we are surrounded by so many people every day, and we can't know enough about anyone (except a select few "friends"), so we strive to fit in, but stand out from the crowd. "I'm different!" Brands market directly to this weakness.
b) Ego becomes a factor. Realistically, other than in a forum like CT or Bivouac where this information is relevant and in demand, there's no real reason to publish these experiences publicly. Living in Whistler I get a bit drowned by the tsunami of "Look how awesome my life is" that comes hits SM every change of season.
c) The internet never sleeps.
Lots of people post these things then go back to "normal life", but their posts live on and keep contributing to the idea that this lifestyle is perpetual.
I jumped off the SM boat a few years ago. Personally I have a low tolerance for the endless "look at me" that comes with SM that focuses on pictures (even though I'm sure I was part of it when I was younger, but there was no internet!).
I also don't like that you lose the rights to your images once they're posted. Whether it's me in a special location or a picture of one of my kids, those images are for my circle, not the public at large. I've asked my wife to stop posting pics of our family publicly as well. Lots of not-cool things happen to pics in the public domain, a quick news search will show you.
Last thought: I've seen a lot of promotion of special places in BC (primarily via the BC magazine's SM engine) that urge people to visit locations with stunning pics. Lots of these places are seeing negative impact as they are not managed with this kind of visitation in mind (Keyhole hotsprings comes to mind). Johnson Lake in the Shuswap is actually asking people not to come!
Not a lot of thought is given to the accountability of SM promotion and the impact it has.