Colas like Coke and Pepsi account for over half of all soda sales worldwide, I always found this a bit puzzling since things like orange sodas, cream sodas, and root beer usually taste better than Coke (for this article I will mostly be using the word Coke for simplicity but in most cases what I will talk about applies to Pepsi and other colas from brands nobody's heard of, diet variants will also be applicable). Of course caffeine addiction is a large part of this but you don't see very many people going into stores buying as much 5-hour energy as they can, caffeine can't be the whole reason. When you break Coke into it's ingredients you begin to understand how it works.
There are three main ingredients to Coke. Caffeine of course is addictive but another lesser known effect of caffeine is that it makes you have to pee more often when you drink it. Another main ingredient of Coke is salt which as we all know is something that makes you thirsty. Coke has a ton of salt in it but of course nobody would drink it if it tasted salty so there is a ton of sugar in it as well to make it taste good, most of the time this sugar is high-fructose corn syrup which will destroy your liver over time in the same way that alcohol does, but in the case of diet sodas this sugar takes the form of some artificial sweetener that is a completely unnatural substance invented in some lab and will probably give you cancer. These drinks are designed to make you thirsty, in the case of regular Coke the only thing that will stop you from drinking it is the fact that the high-fructose corn syrup will eventually make your stomach feel full, but with diet sodas you have no chance since the artificial sweeteners won't fill you up at all, the only things that will stop you from drinking Diet Coke once you've started are self control or running out.
Of course you could look at this and think that it is just a coincidence that Coke is make out of things designed to make you thirsty. This may have been true back when they first invented it over 100 years ago, but they know very well now what they are doing. Back in the 80s when Coca-Cola came out with New Coke the biggest change they made to the recipe was increased salt and increased caffeine, they wanted to multiply the thirst causing effects in New Coke so that people would drink even more of it.
Of course sodas without caffeine do the same thing, most of them have a ton of salt whose flavor is hidden by sugar, soda companies don't want to quench your thirst they want to multiply it. I hope now that you know this information you will take it into account next time you drink a soda and have the strength to only drink one, or even pass and just drink water, the best drink