How come there are many countries with 100% renewable then? Big, small, rich, poor; we have many examples of different characteristics and still we get the nucl

How come there are many countries with 100% renewable then? Big, small, rich, poor; we have many examples of different characteristics and still we get the nuclear vs coal debate as those were the only options. Is it really that expensive, how come 3rd world countries can afford it? I think it's more about politics than feasibility.