Probably just due to manufacturing issues or Chevy didn't have a need for a car that sized right away in 1988. There were no sedans in 1988 only coupes. Sedans started in 1990 so that might have something to do with it. GM had a lot of issues getting production going with these cars back then. Doraville, GA is where the Cutlass Supreme and later the Lumina in 1990 were assembled. There was a massive retooling going on and there were issues on the line. These cars were all new and GM already put billions into getting these cars built.
GM did have the Beretta at the time, so the need for another coupe in 1988 probably wasn't too high on the list.