Question

Why is southeast asia's longest rivers are found on the mainland and not on a island?

Answer 1

The regions mainland are is significantly larger than even the largest island, Borneo. Also, some rivers on the mainland flow long distances through china before they even enter Southeast Asia

Answer 2

Southeast Asia can be studied by dividing up the realm into two geographic regions: the mainland and the insular region. The mainland borders China and India and has extensive river systems. The insular region is made up of islands and peninsulas between Asia and Australia, often with mountainous interiors.