This is probably related to the neural systems for olfactory fatigue, eg why you stop noticing certain smells that are constantly present like your own body odor and the smell of your home/room
There’s a very good Wikipedia article that explains it much better than I can. But taste and smell are closely linked and the sensory systems become fatigued from overindulgence somewhat quickly. Conjecture but the massive amount of flavoring and sweetener in modern beverages is probably a factor in hastening this process