Why is that only some countries are joined in the developed countries?

Only some countries are classified as developed due to a combination of factors such as economic stability, industrialization, infrastructure, education, and healthcare systems. Historical context, including colonialism and resource distribution, also plays a significant role in shaping a country's development trajectory. Additionally, political stability, governance, and access to technology contribute to the disparities in development levels among nations. Overall, these factors create a complex environment that influences a country's ability to achieve and sustain development.