In Western cultures at least, and probably in many others as well, there is a strange relationship between humans and their food. Specifically, the consumption of nutrients and calories, born out of survival instinct, has become an art. People make their careers not out of just turning raw materials into food, but doing it in the most tasty, artsy way they can. We have a culture of food-- first dates are always a meal or at least coffee, holidays are celebrated with feasts, people bemoan the loss of the "family dinner." We love to eat. We are even, one might argue, obsessed with eating. Keep in mind I am making gross generalizations and there are many people to whom this doesn't apply.
In primitive times, it made sense to celebrate food. Food was a sign of status, of privilege, because you had it. Now, the vast majority of people (in the Western, developed world) has basic food supplies. But instead of simply not celebrating with food, we celebrate with fancy food, tasty food, expensive food. We upped the requirements of "feast food." But we still love to eat, and thus, the rampant obesity in both this country, Canada and the UK and, to a lesser extent, mainland Europe.
At the same time, exercise is a chore. Again, generalizations, focusing on the average schlub and not the super athletes. We try to figure out times to cram in a walk or a trip to the gym. We avoid it if we don't feel like it, or if it's a holiday. If we excercise, it is because our doctors told us to, we want to feel better about ourselves, or we want to look better for the opposite sex (or the same sex, as the case may be). We tend not to do it because we want to. It's not pleasurable the way eating is. Is there "comfort exercise"? Do people ever say to you, "I can't stop exercising, I only do it because I'm stressed out?"
And yet, we need exercise as much as we need food, and in this culture, one is vastly more preferable and thus more available. The roles really should be reversed-- eating should become a maintenance operation, and exercise should be fun "family time." That's not going to happen though.
What could happen is that instead of the concept of a gym membership, where you pay a huge sum and then invariably stop going, they should have a gym that's more like a restaurant. You can go in and pay a little fee for the use of the machines for a workout of a given length of time. Include pay showers and rentable lockers, and put them everywhere, with nice long hours instead of the whole "closed at seven" crap. So I can stop by while running my errands, if I have the time, and pay $5 to work out for half an hour on the Stairmaster. No commitments, I don't get guilty if I don't come in, and if you could make them like Starbucks, put them everywhere, people might be more inclined. Especially if it was inexpensive. Maybe offer incentives, or have a "social room" and a "non-social room," so that those who wish to shoot the breeze can do so and those who wish to just work out quickly can also do so. And make the air very, very dry, but offer free camel packs (see picture) with a small charge for the mouth thing so you have a new one, so you can drink water as you work out. That will cause sweat to evaporate quickly and make people more comfortable.
Make it as convenient to exercise as it is to eat, and people may want to do the former a little more often. Then again, gyms pretty much LIVE off the guilt factor-- my concept might not work economically. They would have to open the first one in the upper-middle-class residential area of a big city, since city types are more likely to want to go to a gym.