I have gone on a of number cruises, especially on the Alaskan cruise and Panama cruise the one thing I never heard from anyone was "I wish they traveled faster.".
There is a number of trips that a slow and quiet trip would make for great fun.
During the uncertainty of when/if ports would reopen across Europe, some UK cruise companies went so far as to simply offer "cruises to nowhere".
I.e. they would set off the usual ports, but not head for continental Europe, just sail out to a calm spot with agreeable climate and hang out there for a while.
Because I can't imagine people are happy to pay to sit for a week in an industrial dock in Portsmouth. Also sailing to warmer waters means you can sit on the outside deck/balcony and enjoy the sun. Again, not exactly the things UK ports are well known for.
I'm going to guess that there are laws that make that pretty undesirable. For example: There were (and maybe still are) gambling ships on the Ohio river and on Lake Michigan - all of which docked in Indiana. Unfortunately, such gambling was illegal in Indiana. The ships had to leave dock and go out a little on the water. Suddenly, the gambling was legal.
There are probably dozens of these laws that encourage leaving the dock, especially if you are going into international waters instead of simply between states.
There is a number of trips that a slow and quiet trip would make for great fun.