Why? The Democrat Party is not a public organization. It is an association of like-minded folks. But, the association has published rules and regulations and the folks who join are subject to that. The super delegates are part of that. Their job is to make sure that the candidate that the Democrat Party feels is most likely to prevail in the general election will be the nominee. While I like the Repub system better, the Dems are always about control (of government, of you and me, etc.) so it is no surprise that they control their nominee. It is progressive, not democratic.
But they do use the public voting system for their "elections". If they don't want a democracy (yes, yes, I've heard all the democracy/republic arguments - I'm speaking in general of rule by the people) then they can host their own voting without getting the county and state boards of elections involved.
SO.... while Dems want a purely democratic system for the election, they want a non democratic system for the primaries ?