Bill Clinton gave several speeches, e.g. the 2011 NYU Commencement Speech where he points out:
“The problem with all countries that have great systems is they get long in the tooth. They become so successful that those who run them are more interested in holding on to their positions than advancing the purposes for which they were established, more interested in maintaining the gains of the present than achieving even greater ones for our children in the future.”
Since polls indicate the Bernie Sanders has a better chance than Hillary Clinton to be successful in the general election, Superdelegates that continue to support Hillary Clinton show that they are more interested in holding on to their positions than advancing the purpose of the Superdelegate system, namely to deprive the nomination to insurgent candidates who might not be successful in general elections.