What makes you think they didnt?

Post war reparations from Japan took two main forms, very similar to what was extracted from the European Axis. The first being cash or free goods and services to both former combatant nations, and former Allied POW's, or the confiscation of money or other financial assets held overseas. The compensation for forced labor by POW's was actually then coordinated by Japan making payments to the Red Cross for distribution.

The other was the literal transfer of physical assets like remaining machinery, vessels, vehicles, and the like from Japanese control to other parties. Either taken from Japan itself, or whatever was left in newly free nations that was owned by a Japanese company or the govt, was no longer their property.

The process and parties Japan would be expected to pay and the general amounts were mostly hammered out in 1951 in the Treaty of San Francisco. It both officially ended US military rule in Japan, codified the expectations of the new Japanese govt with respect to honoring things like the decisions of the War Crimes Tribunals, and UN mandates, etc, as well as the financial aspect.

Over the course of the 1950's then Japan concluded agreements with nations like The Philippines, Vietnam, and Indonesia to work out payment in either cheap loans, outright payments, or goods and services as a result of occupation of those territories. Though the value of Japanese assets in the former occupied nations that was transferred tended to be worth more than the new monetary compensation which was stretched out over 20 years of payments essentially. To put some hard figures out the payments for Burma, The Philippines, Indonesia, and South Vietnam totaled about 1Billion USD collectively in 1950's dollars.

While for assets held abroad in one form or another

According to the Japanese government’s research, as of August 1945, the total amount of Japan’s assets abroad was US$23.7 billion, including: US$4.391 billion in Korea; US$2.658 billion in Taiwan; US$9.158 billion in North East China; US$3.465 billion in North China; US$2.295 billion in Central and South China; US$1.751 billion in other areas. https://www.loc.gov/law/help/pow-compensation/japan.php

It should also be noted that there were exceptions, the USSR was not a party in San Francisco, nor was the PRC. China and Japan would not formally settle claims until the 1970's and a Joint Communique between the two was released wherein China renounced claims.

There were several other notable issues that were not covered specifically which have since caused tension, notably Comfort Women from occupied nations and any compensation due them directly and specifically. While the framing of long term or low interest loans as 'quasi reparations' would be a sticking point at times, especially as relates to South Korea. That also doesnt mean that private citizens have not occasionally bring new court cases against either Japan itself or private companies for compensation, and while most of the time Japan has been able to point to followup treaties with nations that barred further new claims, occasionally a court will side with the person bringing the suit and these cases can drag out for a decade or more. Nor was this only from Asia, Western POW's have brought cases occasionally as well.

Text of the Treaty of San Francisco if you would like to read it.

I would give this wonderful article compiled by the Library of Congress a look through it examines much of both the process, and context or various forms of payment from Japan, and their challenges afterwards. https://www.loc.gov/law/help/pow-compensation/japan.php