As I said... it's complicated.
Indeed, is is a complicated issue. US Labor Laws play a role in the issue. And, that then gets politics entangled in the issue.
It is a fact to which I will testify as a result of many conversations with cruise ship staff members from Asian countries, particularly. They work on the ships for whatever the cruise line pays, for whatever duration their contract requires, for a variety of reasons. Number 1 is almost always to be a better provider for their family than they could be if they sought employment in their home country. Number 2 has consistently been their desire to earn sufficient funds to open a business in their home country. The small basic salaries that these good people earn are augmented by "some fringe benefits" that most cruise guests are unaware (and probably don't care).
Gratuities that the crew receive are significant to them. Those gratuities are on top of their basic salary. I always plan on offering additional tips above what my shipboard account is charged for those crew that have earned it. When one takes the per day gratuity charge and break it down into how much each of the main staff members that serve one: it's a shockingly low amount/person, in my opinion.
It hurts my soul when I learn of or witness a fellow guest not offering an end of a cruise gratuity to a Steward/Stewardess that has worked their heart out to serve them. And, that situation has become more commonplace than not. Last night of a cruise, I usually delay my departure from the dining room just to be a "people watcher". My most recent observations: more and more people leave their table without a word or an envelope, etc. to their Stewards. There also seems to be more guests than usual who choose not to dine in the MDR that last night.
Maybe my thinking is influenced that, like rail travel in the 1950's and 1960's, I came to learn what was a proper practice when I began to cruise in 1970 and the years that followed.