Mind is like a bird which can teleport. Those who dream with open eyes will agree that they have traveled more within their minds than in the physical world. Now, why don't we give the same amount of work to our body, I guess, as it has been already pointed out in other responses, is our inclination or dependency on technology.
Let me share this small habit that we have made within our family of four. I may not wish to give myself a tag of lazy everytime, but we have made this habit that whenever my brother and me are in different rooms and somehow we cannot hear the shout-out of each-other, we don't usually make efforts to walk to that room and instead call each-other on phone to ask if there's something for which I should walk to you. Sometimes, when we have too much to talk, we may simply shout like 'please pickup that call from me' and then we will just have a little conversation that saves us from making many rounds for small talks. You will call it laziness, I may call it being more or less, both lazy and productive.
Well, that's just an example. The point is, we have some mode of technology to make things easier and quick for us in one way or the other. Because we know that we have access to these benefits, we begin to be a little or more careless or carefree. People who live in cities may have started loving online shopping and home delivery more because it cuts the crap of bargaining with shopkeepers as well as carrying the shopping bags all the way to our home. Without any doubts, technology is great and makes it easier and convenient for us.
But then, if we think of it by adjoining our little dependencies on technology as in whole, we may realize that the fat we are putting on might be an effect of this convenience. The amount of people who boast about gymming and fitness don't really make efforts in the gym, as they eventually find it hard to make efforts. It looks way more easy and smooth on a television screen. Why not just sit on that sofa in your bedroom and watch movies rather than stressing your body till tiring?
Usually, people begin to have that overshaped belly as they start nearing the age of 25 to 30. An average person who may look weak or slim otherwise may also be having, more or less, a bumping belly. Blame it on our schedule, our laziness or our dependence on technology for even the most simplest things, there's really something we may not doing right. In fact, the quality of life also decreases for many as their health doesn't go good with them, which eventually affects our mind as well.
"Your value does not decrease based on someone's inability to see your worth"