The money supply was tight, and Koreans had not been saving. Rhee's administration had relied on his ability to redirect US aid, and its reduction threatened his political system. The later 60s saw politically savvy business and a hard-working middle class. Woo writes, however, that once in motion, Park's authoritarianism moves to a nationalistic drum. Korea moved to industrial deepening, building basic industries indespensible for defense.
Steel is a metaphore for self reliance adn national security.
With the declining of US international prowess, Korea industrialized, and protected its infant industries, with a perceived security threat. Taiwan's political character was more stable, and it did not worry as much about its military. These two factors help to explain why it did not fluctuate as much in terms of development strategy as Korea. A swith to a deeper ISI would have been very drastic, and had visible environmental impacts.