That and with most of the major cruise lines deploying newer, larger ships in 2020 and beyond, they have an opportunity to move some of the smaller ships to new ports that can only handle smaller ships (ie. New Orleans because of the river, Cuba, Panama Canal, Hawaii, Alaska). Plus, Galveston sailings have been been some of the most discounted cruises for the last while (I keep my home base in Texas, so I watch the fare fluctuation out of Galveston on a weekly basis), so there's no loss in going to a smaller schedule out of a new port with a motivated client base during a time of the year when most locals are actively looking to get out of town (and in many cases - go to Disney).
The announcement was on every local NOLA and Gulf Coast broadcast the day this was announced, so I bet many of these sailings sell out quickly - especially that Panama Canal itinerary and possibly the first sailing that includes CC.