Because no one serious wants was allowed by the DNC to run against an incumbent.

Fixed that for you.

Nothing conspiratorial about it. Anyone with half a brain could tell from their tradition of not holding a primary at all when there's an incumbent, as well as their stacking the deck in favor of their chosen candidates in the two previous ones.

You're acting as if the DNC is a political party that only does what the voters ask for, rather than a for profit private corporation, which is what it's legally registered as and behaving like.