Why are there only clubs from a few countries in the East Asia region of the AFC Champions League?

This is because some countries are not eligible to participate due to insufficient professionalization process, insufficient league scale, and insufficient stadium hardware scale to meet the AFC’s evaluation requirements. Every year, the AFC evaluates leagues in various countries and regions. Only those who pass the evaluation are eligible to participate in the AFC Champions League or the AFC Champions League qualifying rounds. Some countries do not have enough evaluation scores to participate in the AFC Champions League and can only participate in the Asian Football Confederation. Cup Winners' Cup, for example, Liaoning in 2010. At that time, China's quota for participating in the AFC Champions League was 3+1. Liaoning had to participate in the play-offs. If it did not pass the play-offs, it would have to participate in the Cup Winners' Cup. Liaoning did not want to participate in the Cup Winners' Cup, so it The play-offs were given up. There are many clubs from countries such as Singapore, Vietnam and Laos in the Cup Winners' Cup. This Cup Winners' Cup is equivalent to the UEFA Cup under the UEFA Champions League.

So the level of the AFC Champions League is still the highest among all Asian club competitions, and not just any country can participate.