Why is/was there no diesel convertible made for the US market?

I know many other countries have diesel convertible models we don't have but still, there are a few occasion where diesel engines could have been offered with convertibles but were not (in the US). For example, the 80s Buick Riviera and Cadillac Eldorado came with optional diesel engines and optional convertible tops but never the two combined. Another is the VW cabriolets/cabrios. The were convertible versions of the rabbit/golf. The non convertible version could be had with a diesel but the drop top couldnt. Only a few SUVs got the option of having both. Anybody know the explaination?