“oil-rich Dutch East Indies”
Compared to the United States, the Dutch East Indies were NOT oil-rich. The Dutch East Indies produced 7,262,000 metric tonnes of petroleum in 1937. That is only 5% of what the United States produced in the same year.
That the relatively backwards East Indies didn't produce much isn't a surprise. Japan was interested in what was still in the ground, not what had already been pumped.