I include the Reatta in the What Were They Thinking set of posts not because the styling was defective, but because it was a marketing mistake. The Reatta dates to the 1981-1990 Roger Smith era at General Motors. Smith saw his mission as stirring up the corporation through reorganizations, purchases of other companies, and the increased use of high technology. Nothing wrong with those ideas in theory, but not all theories are correct. Also, many observers thought that Smith made many mistakes trying to implement his changes.
As the link to Smith indicates, GM was staring to lose money at the start of his tenure as Chairman and CEO. And it was not in good shape when he left. I was a data vendor to GM (demographic/household/income forecasts) during the latter part of his era, and more than once the money owed me would arrive towards the very end of the 90 day payment obligation period. So if the GM was not doing well financially, then why was money being spent developing and marketing an obviously low-volume two-passenger car?
The Reatta link above mentions that the sales expectation was 20,000 cars per year. As it turned out, not many more than 20,000 Reattas were sold over the entire four-year production run. Among the problems was that while the Reatta looked sporty, it wasn't a sports car; that ruled out potential sales to sports car fans. While it was properly a luxury "personal" car, the fact that it only had two seats meant that its appeal would be limited. For instance, Ford's original Thunderbird was a two-seat sporty (but not sports) car, and its sales were disappointing until it was redesigned to carry four people. Buick marketers and planners surely were aware of this, but forged ahead anyway.
As for styling, the Reatta was developed near the end of Irv Rybicki's time as head of GM styling and perhaps some work was done after Chuck Jordan succeeded Rybicki. This was a time when GM stylists tended to prefer simple, clean designs. Often this preference resulted in cars that looked bland, were lacking in character. So it was with the Reatta. It was professionally styled, having no obvious defects. But it wasn't memorable and failed to seduce potential buyers by its appearance.
For some reason good money followed what was clearly a bad investment. A convertible line was added for 1990-91, but fewer than 2,500 were produced.