Yeah I get that, and used to think the same thing. Then one day I found out I was type-1 diabetic and decided that diet soda was better for me to drink than the regular versions. After drinking mostly diet for several years now, whenever I try a "normal" one made with corn syrup, that's the one that tastes weird. Of course now that I think about it, diet still tastes kind of weird, but I guess I've gotten used to it, although I will say that I think Coke Zero Sugar has come pretty close to having a "non-diet" taste.
The Sodas made with real sugar still taste good to me (like Mexican Coke and throwback Mountain Dew). Those would my favorite choice if I wasn't diabetic and if they were more readily available.
Speaking of the Diet Dew, it's baffled me for years how the 2nd ingredient is orange juice, but somehow the end product still has zero carbohydrates. From what I know, orange juice is one of the highest carbed things that there is. I guess they must have found a grove of sugar free oranges or something.