Cambodia has fallen behind other ASEAN countries in terms of economic development for a number of reasons. These include:

• The Khmer Rouge genocide: The Khmer Rouge regime, which ruled Cambodia from 1975 to 1979, killed an estimated 2 million people, or one-fourth of the country's population. This genocide had a devastating impact on Cambodia's economy and society.
• Political instability: Cambodia has experienced a number of political crises in recent decades, including the Khmer Rouge genocide, the Cambodian Civil War, and the 1997 coup d'état. This political instability has made it difficult for the government to implement economic reforms and attract foreign investment.

• Corruption: Corruption is a major problem in Cambodia. According to Transparency International, Cambodia is ranked 162 out of 180 countries in terms of corruption perception index. Corruption has a negative impact on the economy by discouraging foreign investment and deterring economic growth.
• Lack of infrastructure: Cambodia's infrastructure is underdeveloped. This includes roads, railways, airports, and telecommunications. The lack of infrastructure makes it difficult to transport goods and services, which can hinder economic development.
• Natural disasters: Cambodia is prone to natural disasters, such as floods, droughts, and earthquakes. These natural disasters can damage infrastructure and crops, which can set back economic development.

Despite these challenges, Cambodia has made some progress in recent years. The country's GDP has grown steadily, and the poverty rate has fallen. However, there is still much work to be done to catch up with other ASEAN countries.

Here are some of the things that Cambodia can do to improve its economic development:

• Invest in education: Improving the country's education system will help to increase literacy rates and give people the skills they need to get good jobs.
• Reduce corruption: The government needs to crack down on corruption and create a more transparent and accountable government.
• Invest in infrastructure: The government needs to invest in infrastructure, such as roads, railways, airports, and telecommunications. This will make it easier to transport goods and services and will help to attract foreign investment.
• Manage natural disasters: The government needs to develop better disaster management plans and invest in early warning systems. This will help to reduce the damage caused by natural disasters.

By addressing these challenges, Cambodia can continue to improve its economic development and catch up with other ASEAN countries.