I thought this would be inherent just on their training? There are many multitudes more Reddit posts than scientific papers or encyclopedia type sources. Although I suppose the latter have their own biases as well.
In fact, OpenAI has made deliberate changes to ChatGPT more recently that helps prevent people from finding themselves in negative spirals over mental health concerns, which many would agree is a good thing. [1]
Companies typically have community guidelines that often align politically in many ways, so it stands to reason AI companies are spending a fair bit of time tailoring AI responses according to their biases as well.
1. https://openai.com/index/strengthening-chatgpt-responses-in-...