(And if you look outside that particular imprint the publisher's politics become even more obvious)
The greatest "myth" I'm seeing in this thread is the idea of objective pop history writers (or readers). All of these works are goods being sold to a consumer audience. Perhaps in decades past, many consumers favored works that expanded or challenged their worldviews. But in today's zeitgeist, most consumers want to read things that reinforce how they view the world already.
Or you'll have to explain why this is obvious.
And that's exactly what to expect from a conservative library! There's no left-wing book, at all, in the shelves and that's a pretty clear sign.
We can't know for sure if the “general topics” are themselves conservative, but the complete lack of left-wing PoV in collection, that doesn't bode well.
As an example, there's this biography of William F. Buckley Jr :https://www.regnery.com/9781610171557/william-f-buckley-jr/ whose blurb reads in part "William F. Buckley Jr.: The Maker of a Movement tells the incredible story of a man who could have been a playboy, sailing his yacht and skiing in Switzerland, but who chose to be the St. Paul of the conservative movement, carrying the message far and wide." (and makes it sound more more like a hagiography, but let's leave that aside).
Then there's https://www.regnery.com/9781610171458/just-right/ with this excerpt from the blurb: "This memoir is full of colorful stories from a man who has been present at nearly every major event of the modern conservative movement and has done it all in a remarkable, multifaceted career."
Also in the same imprint is Rick Santorum: https://www.regnery.com/9781932236835/it-takes-a-family/ about whom I don't think I need to say much more.
I said "obvious" regarding the publisher overall, not just their imprint. You'll notice they have a "Political Books" category (https://www.regnery.com/books/political-books/) in which you might find that their 'Featured Books' include "Unwoke: How to Defeat Cultural Marxism in America" (by Ted Cruz, and please refer back to my comment re: Santorum), "Hide Your Children: Exposing the Marxists Behind the Attack on America's Kids" , "When China Attacks: A Warning to America", "The End of Woman: How Smashing the Patriarchy has Destroyed Us", and "Domestic Extremest: A Practical Guide to Winning the Culture War".
If that's not enough for you, then please consider the publisher's own words: "Want to read conservative books that drive headlines, start debates, and change the course of history? That’s what Regnery books have been doing since 1947." which doesn't leave much room for ambiguity.
specialising in conservative books isn't the same thing as catering primarily to "right wing culture warriors", in the sense that any book from their collection can be assumed as biased.