people don't like the lexmark versions quite so much?
I think that this is true.
If somebody wanted something fresh and new, they would buy a Unicomp.
If they are looking for a seasoned warhorse, they want it to look "Bad-Ass"
The Lexmark is probably just as good as any other blue label, including IBM-branded ones, and the quality control is surely better than current Unicomps. But the blue label itself indicates that it is from a date well into the 1990s, and many people may want something older. Also, the 1391401 number is considered the "classic" model, although I think that the metal badges are much cooler.
Personally, I still have a 1991 black (aka white aka beige aka gray) label 1391401 that was my first Model M and I have kept it completely stock. It still feels great and is one of my favorites.