Cuba decided to send troops to Angola in November 1975 for several reasons, including:
Ideological alignment: The Cuban government was aligned with the Marxist-oriented People's Movement for the Liberation of Angola (MPLA), which was fighting against the pro-western National Union for the Total Independence of Angola (UNITA) and National Liberation Front of Angola (FNLA).
Internationalism: Cuba saw its intervention in Angola as part of a broader struggle against imperialism and colonialism, and as a way to support a fellow socialist government.
Strategic interests: Cuba saw its intervention in Angola as a way to expand its influence in Africa and to counter the influence of the United States and South Africa in the region.
Diplomatic pressure: The Soviet Union, which was a key ally of Cuba, had been pressuring Cuba to intervene in Angola to support the MPLA.
Overall, Cuba's decision to send troops to Angola was motivated by a combination of ideological, strategic, and diplomatic factors. The intervention was part of a broader struggle for influence in Africa and the Cold War more generally.