For those who feel 'identified' by going to purser who is really about six people depending on shifts, why not write Princess and ask them to give you a 'tip' selection option prior to boarding. They could make it an option on the web page for registering / via your travel agent. Its an idea.
believe me, unless you make a lot of noise for attention, nobody is going to remember who you are when you spend five minutes getting your account adjusted.
What is true is that a lot of folks were either not informed what guidelines were prior to a trip or decided the overall trip was a disaster so nobody gets a tip or thought the price included it.
By overall charging to account the cruise line in one way is wanting to ensure staff get an uniform ammount at end of cruise.
By allowing you to adjust , you are being given flexibility and your choice.
Try taking it off in Europe from your hotel bill or areas that just add it on period. A lot of resorts tell you your bill will include an automatic gratuity and your bill is considered unpaid if you try to reduce it.