Think I just found the primary reason for it: "It’s Star Wars: Galactic Nights, taking place in the midst of this year’s Star Wars Celebration!"
https://disneyworld.disney.go.com/e...actic-nights/#/drawer=drawerPartyDatesDetails
That's right. SW Celebration is going on at the same time and they want in on the action. They'll be at SW Celebration during the day so why not make the price point higher than 1 day at MK in the evening. Why should downtown Orlando get all the $$$?
It was either Disney put together an evening package or the organizers do it (like the organizers of Gay Days create their own after hours party). Either way, Disney gets paid.