Great questions! Let’s see how we can address them one at a time.
1. Why don’t we “have it”? Or better put perhaps, why is this particular motion more challenging for more people, on average?
The simplest answer that I have right now (I’m sure I’ll learn more as time goes on and as a result, will have better answers in the future I hope!)…is that we don’t have it because we don’t ever access it or use it. It’s that simple. This is a motion (of the hip) that is completely opposite of how we typically move, and especially, how we typically sit: at our desks – in our cars – on our bikes. Etc..
We don’t have it because we don’t use it.
2. Why do we need it? Well, that’s a slightly more challenging question to answer. But I’ll give it a go.
You are all (perhaps painfully) aware of how much emphasis I place on motor control and movement “patterns” – on performing basic stability “skills” as correctly as possible…
…so that “correct” patterns can be developed at a basic level, first, and then progressively demonstrated at increasingly higher levels of complexity and dynamic load.
This motor control, which is also commonly referred to simply as “stability,” happens primarily in the brain, and also in our joints. Contrary to some previously held beliefs, it’s never only a top-down or bottom-up kind of thing.
When you are doing a very basic movement to build stability of the trunk or the hips – such as a basic bridge or clam exercise – what you are (hopefully) doing is correctly patterning from the brain to those connective tissues and joints involved, or vice versa, from those joints and connective tissues involved, back to the brain.
Done repeatedly, correctly, over and over again…you’re creating the right kind of “wiring” that will hopefully lead to balanced stable movement, which in turn leads simply to muscles and joints doing, and being asked to do, what they are designed to do.
Simple enough, right?