Boston to Portland (ME) via Cruise and Day at Sea?

[colliercruiser]

I'm trying to make sense of a Summit Canada/NE itinerary in Oct 2022 which leaves Boston at 6 PM and arrives in Portland, Maine at 8 AM, BUT there is a day at sea in between. You can drive a car from Boston to Portland in less than 2 hours, and other sailings leave Boston and arrive at Bar Harbor (north of Portland) the next day.  So does it make sense to have a day at sea between leaving Boston and arriving in Portland?  Seems that the ship would just be taking a very slow "journey to nowhere" for a day.

[cruisestitch]

Could be that the port of Portland has schedule conflicts.

[Arizona Wildcat]

Definately a slow boat.  Have done that.  The reason given was scheduling dockage.