The majority of Asian countries perform poorly in international football competitions because football is not as popular of a sport as it is in other parts of the world. When a sport such as football is popular in a country, kids will grow up playing with friends, they will join teams early on, and hone their skills over a lifetime. These countries have a large pool of talent to pull from.
In countries where football is not a popular sport, kids who may have been great football players end up doing something else. They may be great tennis players or swimmers instead.