Why do people buy diet soda?

I work as a pick up person and I happen to notice one of the common customer purchases is diet soda (the twelve packs to be exact). I had a few consumers literally buy 14 twelve packs of diet coke... and yes, it was a pain walking the heavy load to their car. The point is, do they know they are increasing their cancer risks? If they do, why do they still drink it? I guess it's similar to cigarettes where you know it can kill you but you use them anyway but diet soda isn't even a controlled substance. Same with people buying keto. That stuff is so bad for kidneys. It's kind of sad that instead of working (exercising and eating healthy) to lose weight, people would rather take the easy way even if it means shortening their lifespan. I still have a high metabolism so I don't understand the predicament most people go through; however, people are shortening their lifespan to make themselves look good.
Why do people buy diet soda?
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