John McWhorter has an explanation:

Racism is, I suspect, part of the story here—but not in the way we’re supposed to think. Is there a part of Rangel that has supposed that the ethics are fundamentally different for him since his nonprofit is devoted to battling the legacies of institutional racism? The CBC traditionally calls itself “the conscience of Congress,” and in its public statements and activities often functions as a kind of alternate NAACP rather than as a generator of legislation. Under this frame of mind, there would be little difference between serving “myself” and serving “my people.” Surely to combat racism is a greater good than any other. My nonprofit is the fight against racism. The fight against racism is me. Me is the fight against racism. Why not improvise a little, especially if no one is looking?
This seems to be the only kind of explanation, given data in so far, on Maxine Waters’ transgression. She consults with Barney Frank about the propriety of setting up a meeting over bailout funds between Treasury Secretary Henry Paulson and a consortium of minority-owned banks when her husband was a stockholder in one of the banks. Frank says it isn’t a good idea, and yet she goes ahead with it, right down to the meeting itself being populated mainly by reps of the very bank her husband was involved with?
To suppose she was concerned solely with preserving her husband’s stock returns may have its kicks. But a better fit with her entire career’s mission, not to mention her current justifications, is that she felt that saving minority banks was a greater good. It’s not hard to see that she, in that position, would readily use as a main conduit the personal connections she naturally had with people at the bank her husband was involved with.
Especially if no one was looking. After all, look at what she has sometimes done even while people were looking—I will never forget her dancing on camera with L.A. gang members.