Some people like to reduce it to the fact that they're simply a "product of their times." I think that's a cop-out. Washington's book is an interesting study because it suggests, in many ways, the perpetuation of a black underclass - so to speak - while reinforcing white hegemonic aristocracy (evolved into accumulation of capital). However, he also undercuts black inferiority while simultaneously appearing to imply it; we discussed it today in class, and our professor (who is African American) actually tried to suggest that, at this moment in history when the book was published (1901), Washington didn't have much choice in what he could say.
I'm not saying that he would get in trouble for saying something more radical (W.E.B. DuBois said things far more inflammatory); I'm saying that, at this moment in history, he wanted to try and offer blacks a pragmatic means of social mobility that would allow them to life themselves up by their own bootstraps, basically. Unfortunately, doing so simultaneously reinforces the exact same organization of labor that establishes them as an underclass.