DL passes out a paper menu on international and TCONs in Y to speed the process. And every US airline at least has the drink and food menu in the airline magazine and sometimes on an additional standalone insert in the backseat pocket -- it's just no one bothers to read it until the cart gets to them which slows the process down because they have to fish out the menu and stare at it.

I would imagine a good deal of it is pure efficiency. It's not efficient for an FA to continually walk back to the galley to get a round of drinks. It's far more efficient to have everything right in front of them to accommodate the request on the spot and be able to provide them at the same time.

Plus you eliminate randomness in drink orders that cause bigger deviations in service time -- if you follow the same process every time you can have a pretty accurate idea of how long it takes to serve F&B on a full plane by plane type.

If you allow personalized ordering, the randomness of passengers on a given flight could cause dramatic deviations in service time because the passengers are unlikely to order in an efficient manner (aka all at the same time) -- they are instead likely to be staggered which could result in slower service times.