Babies start their lives with very limited movement abilities, and yet they can learn to crawl and walk largely on their own. They focus their attention on themselves to wire up the neural pathways that allow them control their bodies and feel what their bodies can sense. Learning gong fu as an adult requires a similar sort of focused attention to develop the body control and awareness that will allow the skill to manifest. The mindful physical practice establishes the movement foundation that allows the art to be expressed.
Children are still developing. They are itching to explore the world and learn, which requires that they become mobile. Freedom to move and explore is a huge deal, so children put serious effort into the task of learning to move. Adults with their busy lives have other concerns that can take away their attention from the learning process. Usually by adulthood, learning an art is just a casual hobby done in limited free time, so staying engaged with the learning process is a challenge. But being present and immersed into practice is the one sure way to achieving anything beyond a superficial level of skill. To achieve a deeper level of skill, we grown ups must let go of the external distractions (as much as we feasibly can anyway) and actually focus our attention on the task of learning. If we treat learning as an important task, we can reap the rewards of deepening the skill.
Babies start with no assumptions or foreknowledge about how to move. They learn what works and doesn't work through experiential experimentation. And since they are not yet strong enough to move with dysfunctional movement patterns, they have no choice but to move in harmony with their body structures. An adult comes into the learning process with preconceptions, and usually does have the strength to move in dysfunctional patterns. Learning gong fu as an adult requires returning to the beginner mind of a child. Half the battle is throwing away the assumptions and past experience and immersing the mind into the process. Keeping the mind present is only way to reconnect oneself with the body senses and to learn to move naturally without strange compensation patterns.
When babies learn to crawl and eventually walk, they need to sense where their base of support is and where their balance points are that allow them to move. Those are the same foundational movement skills a martial artist would need. Martial artists need to be able to move efficiently. The requires good balance and body awareness. In any art, you need to know where your base of support is that gives you stability, and you need to know where your points of mobility are so that you can dodge, pass guard, pivot into your opponents space, throw, strike, etc.
Learning new movement skills can be a frustrating, but rewarding process. My boy loudly vocalizes his displeasure with being unable to do something he wants to be able to do. But he always has a huge smile once he figures it out. I'd say a lot of adults experience similar (though usually not so vocalized) cycles of frustration and accomplishment.