I was wondering the same thing as we sailed with Celebrity last year out of Puerto Rico and bought the classic drinks package before we went. What a great idea - it certainly saved us a ton and made it so much easier when ordering.
The bar/beverge staff got to know who you were and what was your favourite tipple and how you liked it served.
Also gave you the opportunity to sample new cocktails as well which if you had to pay for each one and were not sure whether it would be your cup of tea, worked very well.
Shame Carnival are not offering these - will seem most odd to have to go back to 'pay as you go' option.