system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Undecided delegates- What/Who are they, why are they important, and why has the DNC said to stop showing them?

Why/why won't they vote for the most popular candidate?
gpt
They're a set of delegates who haven't been pledged to represent any specific voting sector.  Most delegates are pledged, and must vote the way the voters they represent go.

They're meant as a way to give some inertia to the standard views and ensure that a fringe candidate is really electable.  They usually go for the establishment candidate and it presents a barrier to opponents getting in.

For example, if there were four or five democratic candidates then they'd mostly swing towards the most establishment candidate.  If there's a popular nutbar in that group, then that nutbar has to beat the superdelegates to get nominated.  He can't just skate through  and win.

The DNC wants to stop showing them because they haven't actually voted, so it's misleading to show them on the list.  It makes it look like Hillary's lead is overwhelming, rather than just very significant.  It also makes it seem a little less like the DNC is trying to swing the vote for Clinton.

Think of superdelegates like a handicap in sports, except it goes to the favorite.  It ensures that an underdog really has to whomp the favorite in order to win.  This prevents popular but unelectable candidates from stealing the nomination and then losing the general, which has happened before.