Probably somebody out there completely understands back pain, but I haven't been able to find them, and it's not me.
Nonetheless, certain things are obvious.
The low back is a weak spot in human anatomy, because we vertically load weight on it. It's originally designed to hang weight anteriorly (think of a horse), to provide flexibility to the trunk, and to armor the spinal cord. Due to this vertical loading, problems develop, such as bulging and ruptured disks, vertebrae that slide around on top of each other (spondylolisthesis), and compression fractures, where the weight causes vertebrae to implode.
Another obvious thing, at least to me, is that we need good posture during the day. This involves the appropriate curvature of the spine, especially the lower spine. We tend to sit in chairs a lot, slumped, with the loss of that nice, concave shape that keeps our lower spine happy.
Of course we slump around in a lot of places, but one place we do this a lot is in cars, and other vehicles. We slump with our lower backs curved out toward the seat, and this tends to make the soft bits of the lower spine go in the wrong direction. With all the time we spend in cars, I think this is a major contributor to low back pain. Even cars with so-called "lumbar support," in my view, do not do enough to support the anatomical curvature of the low back.
What I do is use a 2x4, about 12 inches long, behind my lower back while I'm driving. (Note that this is a horizontal position, not a vertical one!) For me, this does a tremendous job of reducing back pain. I think it's even therapeutic: when I feel an episode of back pain coming on, I pull the 2x4 up behind my lower back (it tends to drop down while I'm driving) and reconstruct the lumbar curve.
Because a 2x4 is rather hard, formerly I would wrap it in a small towel, and then wrap the towel in duct tape, but I find I don't need it any more.
The bottom line here is that just like arch support for feet, we need to create good lumbar support for our backs, because the world is set up to make our backs hurt.