Joseph,
I included the second reason because when I discuss politics with my fellow frum Jews I hear them making the same arguments, using the same terms, that I hear from conservative pundits on the radio. More importantly, large percentages of my fellow frum Jews appear to subscribe to conservative/Republican political positions even where it doesn’t have a basis in Torah–and is sometimes contrary to Torah hashkafah. For example, I hear people vociferously supporting the conservative positions on gun control, immigration, and climate change despite the Democratic/liberal positions being more in line with the Torah on those issues.
With regard to your last point, I absolutely agree that the overwhelming liberalism of secular/atheist/irreligious/Reform/Conservative/OO Jews is due in large part to their obtaining their news from liberal media. I would only add, however, that they are also strongly influenced towards liberalism from their college environments where liberalism is even more dominant than it is in the general mainstream media.
We are all influenced by the media we consume and the opinions of our peers and our teachers. A person has to work hard to try to think through each issue independently and even then he can’t entirely eliminate the influence of others.