Because it is as hard for him.
It is as hard for him to attempt to walk as it would be for you to cross to the other side on a thin log 15 feet high over a fast running stream.
He thinks in the now. In the present moment, or Now it is hard to walk for him, impossible perhaps. So why would he try?
His rational mind is not mature yet to predict the future. His brain can not assist him to see beyond a certain point. Without the rational mind, he does not see that the effort he has to put into learning a difficult task will pay him off later. He wants a cause and effect now. If his actions do not give him satisfaction in the moment he will try something else. So he chooses a very smart route. He adapts.
Even though adults have their rational mind developed well, adults don’t act that much different either
We all adapt differently. Some of us try walking with a different gait pattern. Some of us try locomotion with a wheelchair. Some of us have bodies that can not move according to our will at all.