Daily Service Gratuities are always removable, and while the cruise line may ask for a reason you do not need to tell them anything. They are optional in all cases vs a daily service fee. The only main line cruise I believe using a daily service fee is Costa, the other lines they are daily gratuity fees. In 40 years of cruising, 80 cruises I have never allowed a Daily Gratuity fee to be charged to my account.
I tip who I want and when I want, it is not my job as a guest to pay behind the scenes workers or to give them money because they are overworked, underpaid. I pay for cruise, gratuities are always optional and have nothing to do with the cruise lines. If a cruise lines makes Gratuities required I do not book with them.
My last Costa trip they tried to charge them based upon it being a service fee, I did get them removed, but not without a meeting with the Hotel Director & Staff Captain. Move work than most guest would do. I hate cruise lines trying to steal and defraud guest with these fees which are not paid to the crew as guests think.