There are a lot of different reasons why someone wouldn’t just buy a Z06.
1 - They purchased their narrow body before the wide body became available.
2 - The wide body cost 20-30k more and maybe wasn’t in their budget.
3 - Some prefer narrow body over wide body as personal preference but want more power for different reasons.
4 - Then some add supercharger power that can run and/out performs Z06 because they race/track etc.
5 - I like racing my buddy and his Z06 and he gets frustrated when he can't win all the time but just boys having fun.
6 - My car is customized and unique to me and that is important to me and you want see one like it.
7 - Z06/GS are beautiful and have more of a racing look with wide body stance, Stingray is more of a conservative elegant look so whatever one's taste are you can't go wrong.
Lastly, I am that person who wanted more power and it didn’t make fiscal sense when my car is paid for with only 25k miles, love my mods and uniqueness, and lastly can run as fast with a Z06 so I have the best of all worlds and love my car over replacing it as its a keeper. I am not want to chase the next latest and greatest when I am very happy and satisfied with what I have but I did considering the Z06/GS for a minute but my fiscal logic prevailed.
My buddy is the opposite in that he buy and sell and have to get the latest and greatest in which there is nothing wrong with that but I try to not lose a lot of money in purchasing depreciating assets but he doesn’t care so we all just have different reasons on why we do what we do and all of the different reasons is right for each individual as we are not monolithic and have different money strategies, buying personas, budgets etc that drive our decisions. Hope this robust answer helps in response to your question.
Not aware of a "Supercharged" Z51. If you added that, why not just buy a Z06?