The rules are that the executive can appoint judges. Right wing executives take advantage of this rule. Doing the same from the other corner seems reasonable too. The failure to do so means that the Democratic party is incompetent, uninterested in enacting their own alleged policies, or some combination of the two.

Some people say "if you're not cheating, you're not trying" but this is even a level removed. This is a perfectly legal move that they've denied themselves for no material reason.