Availability :) a RTG requires Plutonium 238, which needs to ne created almost on purpose in a nucleare reactor. Not all nations have this ability or they are r

Availability :) a RTG requires Plutonium 238, which needs to ne created almost on purpose in a nucleare reactor. Not all nations have this ability or they are running such expensive programs. Also in the USA they are reserved for programs where there is very little light available