For what reasons could Thailand be described as a developing country in the 1970s? In what ways was it able to change?

In the 1970s, Thailand had a very low GDP Per Capita. In 1970, Thailand's GDP Per Capita was only 192 dollars. For comparison, the U. S. GDP Per Capita in the same year was 5.247 dollars.

Besides, in the 1970s, Thailand was a monarchy where the king at the time: king Bhumibol Adulyadej, had effective powers over the people. Not all monarchies are developing countries, but monarchies and dictatorships tend to be poorer because of the lack of independent judiciary and enforcement of property rights which disincentivizes investment and economic growth.