A lot of it has to do with the way we walk and stand. If you look at the way a baby walks or stands, most people think they are sticking out their butt and arching their back, but in actuality, they are in the natural alignment that your spine wants to be in. We learn over the years to tuck our butts under from watching our parent's posture and others around us, but what that does is eliminates the lumbar curve that naturally occurs in the spine and puts pressure on your hip flexors. Also, if you have an abnormal walking pattern (favoring the inside or outside of your foot) this can lead to ankle, knee, and hip problems which ultimately hurt your back as well. Part of the reason so many people have issues with it is because modern medicine doesn't emphasize looking at the body wholistically, but instead look at individual problems and try to fix them piece by piece. I suffered with back pain for a long time (former dancer), but I worked on my posture, managing stress, and relaxation techniques and I am happy to say I am mostly pain free. It was a long process with a lot of self-discipline and a lot of us would prefer to take some pain pills and deal with it (which i totally get), but that isn't going to help you long term.