For the people who are actually on the DNC rules committee and run the party, the DNC is their social club they want absolute control of. They only participate in elections to fundraise so that they can run ads and take a cut of the ad spend to fund the party and their own lifestyle. If anything, a Trump dictatorship, as long as it allows fundraising and ad spending in “opposition” actually benefits them just fine. And if there’s no possibility of them winning, only the most glassy-eyed cultists remain in the party so no more internal dissent, which is perfect for them.