I think you're right. Leftist Democrats are astoundingly good at getting what they want on the bench: statist, anti-gun, anti-traditional family, pro-choice judges.
Republicans are absolutely terrible at it, and have an awful track record.
What is the difference? Leftist Democrats are very comfortable with the secular humanist ideology of their base, and Republicans are deeply uncomfortable with the ideology of their base - religious conservatives, economic conservatives, combination, etc.
"What is the difference? Leftist Democrats are very comfortable with the secular humanist ideology of their base, and Republicans are deeply uncomfortable with the ideology of their base - religious conservatives, economic conservatives, combination, etc."
And it only gets worse. If the driving force is to defeat Democrats (who still effectively retain veto power), it comes at the expense of conservatism. The more important it is to beat Democrats for the sake of beating them, the less conservative Republican nominees have to be, just as long as they are "electable."