Political parties use to choose the nominees in smoke filled rooms. I don't find this at all surprising. Sanders spent a long term as an 'independent', so why should people whom he never supported or campaigned for, and never helped out, want to support him, and not the most popular candidate in their network, who has spent a political career building alliances?
Political parties exist for a reason, and that reason is not to run complete unbiased open primaries so that anyone may call themselves a party member and get unbiased support of the party.
Parties are biased, there's nothing surprising about that. Both Sanders and Trump are in effect, third party candidates, running campaigns trying to usurp the existing two parties into pouring support into their campaign, because third party runs don't work.
No doubt. Parties are allowed whatever method they choose to select their nominee, including the party elites backing a popular insider.
However, we shouldn't confuse that with a democratic process. We should also recognize that such actions by the DNC would contradict their public statements to the contrary, that they intend to remain completely neutral in the primary process.
If the situation were as you claim, then the parties would not have much of an argument against stronger, populist 3rd parties, because the 2 candidates served to the voters in the General Election would no longer reflect a representative choice of American voters.
Political parties exist for a reason, and that reason is not to run complete unbiased open primaries so that anyone may call themselves a party member and get unbiased support of the party.
Parties are biased, there's nothing surprising about that. Both Sanders and Trump are in effect, third party candidates, running campaigns trying to usurp the existing two parties into pouring support into their campaign, because third party runs don't work.