McConnell is a very vindictive person, that may have been payback for Schumer in July 2007, a year and a half before the end of the Bush administration stating he wouldn't allow Bush to appoint a new justice to the SCOTUS if an opening occurred.
Did Schumer actually ever hold-up a GWBush SCOTUS nominee during that time? No.
Rightwingers seem to have this mindset that "both sides do it" for some reason. I suppose its done to assuage the rightwing sociopathy since they're never going to seek help and fix themselves and become emotionally healthy human beings.