Turn the question on ts head, ask not why you TAKE photo's, but why you LOOK at photo's!
All to easy for the answer to why do you 'take' photo's to essentially boil down to... "Err.well, it's like, err, what cha do, innit?" basically its something to do, and get even more strained from there, as the camera starts to become the focus of attention over the pictures it makes.
Look at face-book or Instagram other host sites, and the proliferation of pictures that would seem to have been taken for no other reason than they some-one happened to have a camera, more still published and promoted them, for little reason more than they can!
B-U-T.. I have to say, that in that contrary to common convention, I actually find more 'casual' photo's taken like this, more stimulating, more interesting and more worth-while, than an awful lot of the cliche'd, over worked 'dross' churned out by photo-enthusiasts.... whilst all too often displaying a far greater degree of purity ad honesty, in the lack of pretension in the inception....
"Oooh! That looks interesting! I'll take a photo of that!" And because they have a camera, they do, and it makes an interesting photo. Rather than camera fan, picking up camera and then asking "OK, so what would make a good thing to take a photo of."... so often followed by... "Oh, that's a bit disappointing! It was far more interesting when I saw it!.... I wonder.... what can I do with it in photo-shop?!"....
So ask why you LOOK at a photo; what in a picture makes it worth your time and attention; what makes it interesting, amusing, entertaining informative... THAT is what I would hope to capture in the photo's I take, whether for me to look at, or any-one else, because ultimately, if no one ever looks at itm no point ever having taken it.....