But what we don't see are the numerous instances of discreet tipping. My hunch is that this occurs much more often than the cases of ostentatious tipping that you describe.
In general, I don't agree with the tipping culture in the United States, especially in the past few years, but when you develop a relationship with a ship's crew member that extends over several weeks, tipping seems quite appropriate and, in fact, difficult to refrain from.