I just left a chain Christian bookstore (one of the major chains) in search of a Hebrews commentary. There were several, but none that made my toes tingle (any suggestions would be much appreciated). When I was satisfied there weren't any I couldn't live without, I looked in the section entitled "OT Commentaries." And that was about the extent of it. There were a few, very few, "Old Testament" commentaries. Not one individual OT book commentary.
I think this is evidence of the sad state of Christianity's understanding and interest in the Old Testament. Unfortunately, Christians will never understand the New Testament as well as they want or need to without understanding the Old Testament.
It's sad, sad, sad.