I know a lot of photographers, part of my job I guess. And many of them carry a camera with them everywhere they go. And I'm not talking about the camera on their phone, I mean anything from a little digital Elph to a D3. It seems that they always want a camera handy in case life presents a perfect moment to capture. It's all very Cartier-Bresson. I myself don't do this and a lot of people find that strange. They constantly ask me, "where's your camera?" And I think the answer has a both practical and philosophical answers.
First is the fact that cameras which would take pictures I'd be happy with are heavy. I'm a stickler for image quality and pixel peeping at 100%. On a trip out west last year I borrowed a friend's G10 to use instead of having to carry my dslr around on hikes. While it was handy and reasonably responsive, I have to admit that I was underwealmed by the results. I was shooting jpeg, which is part of it, but still, the problems were more those of the small sensor and middling optics. If that's the best that small cameras can do, then I think I'm stuck with the big boys. A couple of times in the past 4 years, I've got it in my head that I wanted to have a little pocket camera to carry, but invariably I end up giving the thing to my mother because I never use them when I buy them.
As for carrying around my big camera all the time, no thanks. Most of the time I travel I've got my 5DII, my Hasselblad 501, or Leica on me, and you notice the weight and annoyance of this thing you've got to carry the whole time. A great photographer I met last month has his D700 with him everywhere. Bump into him and there is his bag over his shoulder. But the reasoning here gets me to my second point, and that is what kind of pictures do you take?
Your style and goals as a photographer have a lot to do with it. Most of the people who carry seem to be more along the lines of street photographers. People who walk and notice and capture life. Whether it's a old person on a bench, or an interesting juxtaposition of people and their surroundings, or an interesting cloud formation or whatever. They're not going out to take specific pictures most of the time, they're going out LOOKING for pictures.
Now it's not to say that I don't notice great potential pictures when I'm out and about, it's just that actually taking them is not a priority to me. Most of the time I'm more of a photo Safari one step further removed. I enjoy seeing the potential picture more than taking it. This is because the photos I do like to take are deliberate. If I'm going to take portraits of a person, it's almost always setup in advance and I have a general idea of where and when and what I'm doing. I like to spend time with my subjects, not just catch them sitting on a bench in a visually interesting way from 50 feet and 200mm lens. I interact, I don't hunt. Most of the pictures I take are the kinds of things that could have been painted if it were before the invention of photography.
I also like to take pictures and am careful that I don't get burnt out on it. I was asked a number of times at my sister's baby shower a few weeks ago about why I wasn't taking pictures. Well for one, I don't like taking pictures at events, hell I don't even like shooting 2 people at once. And secondly, I'm not working, I'm there to enjoy my sister's shower. Do people ask a psychologist if they'd like to do a therepy session while they're at their kids little league game. I love taking portraits, and I call myself a photographer, but it's what I do not who I am.
Lastly I think it comes down to my experience, which is that when I do carry a camera with me, I'm generally not happy with the results. They're never up to my personal standards. Go out, shoot 30-40 pictures, maybe you get one or two that are actually worth keeping. Maybe every week you get one that's really superb. Too much work for too little reward in my opinion. I like to know that when I put in effort, I'm going to make progress and hunting for pictures is too much of a gamble for my temperment. Different strokes however and there are a ton of photographers past and present whose work I adore and respect that work that way. The point is that we're not all the same, and that's what makes photography interesting. We've all got different points of view.