The odds were against the potential nominee
Pres. Trump has said that he will not nominate Herman Cain to the Federal Reserve.
Cain, ran for the 2012 Republican nominee but withdrew from that race when he was accused of sexual misconduct. He was also passed chairman of the Kansas City Federal Reserve (until resigning 1996 to persue national politics).
There were reports a few weeks ago, that Cain would not get the full support of the Republicans for nomination in the Senate. Assuming the Democrats would vote against his nomination, the prospects of getting through the needed Senate majority was slim.
Trump never nominated him for the position.