You don't really think they appointed someone as ambassador simply because he'd given a small donation to an election campaign.
Let them enjoy their fantasies.
It never crosses their minds that in the US, there are millions of individuals who donate to campaigns. Obviously, people who care about campaigns are interested in government, politics, social issues, foreign affairs and public policy. People interested in these things are often already working for the government, academia, international business, etc. So, I would be more curious as to how many ambassadors did NOT contribute to one or the other campaign.
An Ambassador makes a decent salary ($150-200K) and the job includes housing, child education, transportation (for the family), great vacation options, drivers, household staff, security and an entertainment budget. Often you meet interesting people but sometimes you have to introduce your wife to a criminal with a straight face.