I wish they would! I gave up sugared soda 30 years ago and gave up caffeine 5 years ago. It's annoying to know you are paying for beverages that you really can't drink. And Dasani bottled water really tastes terrible!
I got hoodwinked on our 2018 trip. We stayed at Pop Century and there was one drink station with Sprite Zero (or Diet Sprite) and one day it was out. I found a nice cast member to ask if she could get it refilled. She came back and told me that they didn't have Sprite Zero, that all of the stations had regular Sprite and that fountain drink was mislabeled! Argh! I felt like Charlie Brown when Lucy pulls the football away just as he's kicking!
I had lost 70 lbs prior to the trip and was making very wise eating choices the whole trip, just to find out someone was spiking my soda with high fructose corn syrup. It still makes me wonder if that was even true. I had a hard time believing that I couldn't tell the difference, but who knows. In my caffeine days, if you had slipped me a real coke instead of diet coke, I would have spit it out upon tasting it. Blech!