Google Flights draws a pretty clear picture of DL's intentions in the MSP-HND market. Try a request for one way, premium economy, non-stop, and view the price graph. The days that premium economy doesn't show up correlate to MSP's observation.
Looks to me this is the precursor to a seasonal drawdown of service in the MSP-HND market - based on the observation of the price that DL is willing to sell tickets for these flights. Looks like the plan is to go to between 2-6 flights per week this fall (depending on the week) instead of the currently scheduled daily service.