Other Asian national teams do not invest so much in the development of football, or football is not their most important team sport, and therefore do not achieve such results in major competitions.
If you talk about South Asia then cricket is only game popular among world's most populous countries aka India, Pakistan, Bangladesh and Srilanka. From far east as you said Japan and Korea are the only strong team. Don't know why China don't have strong football team till date. From middle-east teams do qualify for worldcup but there performance are not upto the mark.