I hate to burst your fantasy bubble, but you are so wrong on so many things with that statement.
You said "The vast majority of the customer facing crew do not get tipped. Those waiters working in the buffet for example."
Wrong! Those waiters working in the buffet can be seen later working the MDR, and vice-a-versa. Tomorrow they may be working the poolside grill, or the International Cafe. They are all from the same staffing pool and will work a variety of venues, all with a percentage of the gratuities. Same with room attendants, who share their gratuities with the support staff that makes their jobs easier, such as the laundry workers. Room attendants can be seen cleaning up public areas when they are not cleaning staterooms.
The crew all work for a base salary. It isn't a high salary, but it is a guaranteed salary. They also get room and board as part of their salary package. This amount is not enough to live on, however - by OUR standards.
Note that not all of the crew are included in the base salary/gratuities programs. Typically only those working in the "hotel" side of the ship are included in this program. Officers, entertainers, accredited mechanics, and other higher level staff sign a contract at a full salary with no part of the gratuity programs, much like on a typical land based company.
The gratuities that responsible passenger pay supplement that base salary for hotel staff, increasing the final income to acceptable levels. Without the gratuities, the crew will at least get the base salary, so they are not, as you claim, "working for nothing".
Most cruise lines that are based in Europe, such as P&O and MSC (for European cruises only), roll the gratuities into the base fare for exactly the reason you mentioned - Europeans don't tip well, and the staff gets stiffed. Many US based cruise lines do the same when home porting in Europe, again because too many Europeans refuse to tip and the hotel staff suffers.
In May 2019 P&O did away with gratuities (SOURCE: https://www.travelweekly.com/Cruise-Travel/PO-Cruises-to-end-gratuities-in-2019) because too many of the locals removed them, so people did not want to work on their ships because of the lost wages they suffered. To attract employees, P&O had to switch or they would not be able to find enough people to run their ships. It's simple economics.