As described in the article, the political bias is intentional. It is the result of (not-so-transparent) ethical guard rails baked into the system.
Is that to say at a higher level "liberal bias = ethical/ok for boat guard rail training material, conservative bias = typically unethical and to be avoided"? I feel like that plays into conservative hands of "they're trying to silence us!" Why do 70,000,000 people vote (R) every year, knowing that the other 70,000,000 (D) think they are "unethical"?
They also typically claim something like "I'm just voting for gun rights" or other very specific carve outs, but if you press them on other things they usually seem perfectly happy to tell you that they think the world is woke and that we need a strongman and all sorts of classic conservative talking points.
Another reason is the religious angle. Millions of americans are enthusiastically, extremely christian, at least as claimed. This includes things like denying that evolution happens, denying the world is more than 6000 years old, sometimes denying that jesus was a white man!, denying that the US is not a christian theocracy, often denying that the new testament supersedes the old testament, sometimes denying women individual rights as free and equal people in society, etc etc etc. Look up the numbers of people who believe in these things.