Amazon was recently polled to be the most trusted institution among US Democrats [0], which comprises the majority of NPR's listenership and donors. They know what they're doing.
(1) That poll is from July 2018, and while that's technically recent, in terms of news about big tech that can affect perceptions, a lot's happened in the last two years.
(2) According to the poll, Amazon was the third most-trusted institution among US Republicans, just behind "military" and "local police", and was the second-most trusted institution behind the military across all respondents. I think you're putting more emphasis on partisan affiliation here with respect to Amazon than the data warrants.
That, or, Amazon knows from history (Google, Facebook, Microsoft, IBM, even going as far back as Standard Oil) that the public trust is not to be taken for granted. They have strong incentives to stay ahead of any negative sentiment that might arise.
[0] http://aicpoll.com/