Why are corvette so expensive if they are terrible cars ?

it's all about status. The coolest car gets the owner more attention. 

I've not heard of them being terrible... but I have heard of most people opting to buy something more luxurious for the going price since a Corvette is more of a muscle/sports car and not really a luxury car... but still priced similarly. 

The new all-electric Mustang starts at $50,000. 

They are cheap compared to European cars with similar performance , like Porsche or Ferrari. However close up you can see the quality of the body work is nowhere near comparable , the Europeans have solid feeling precision parts where as the Corvette is just cheap plastic. Inside is the same story.

Later models have improved considerably , but then so has the price.

They are priced high due to the cost to make the car. The material itself is all made in the United States instead of overseas where it would be cheaper.

Corvettes are cheap for a high performance sports car, especially used ones that aren't sought after as classic cars. 

They are a bargain for the performance and the driving experience that you get.  They are only "terrible" because it is really not a luxury car but an inexpensive sports car.  It is not a Mercedes but it will outrun most Mercedes, in the street or in a track.  Test drive a new one and then TELL US if they are "terrible".

It's a cult thing, besides it's Chevrolets flagship vehicle, true thru the 70s and 80s they couldn't get out of their own way and when they got old they became the poster child for rattles. The newer ones have definitely gotten better but you rarely see them as daily drivers thru pot holes, gravel roads, and inclement weather

Usually..."terrible" in reliability

but not in performance.

They are not terrible cars.

In terms of performance, they are a bargain.  Some of the ones with more powerful engines will beat supercars costing significantly more.  I personally wouldn't want one because they have that hairy chest/gold necklace vibe.