From the NYT:

Members of her staff had said she favored Mr. Hastings. But his position was weakened because he was impeached and removed as a federal judge in 1989 in connection with a bribery case. He was subsequently acquitted in the criminal case.

For Mrs. Pelosi, who had hammered the Republicans for ethical lapses in the fall campaigns, the decision to pass over Mr. Hastings was a sign that she did not relish another battle after the Democratic caucus rejected her choice for majority leader, John P. Murtha of Pennsylvania. (Source)

At least she learns from her mistakes, unlike some in power.