I cannot comment on the quality of sandwiches in the 1980s and haven't found a detailed history but AFAIK there never was a traditional dining car on TGV. At most, you would get an airplane-like meal-tray, as you can currently get on the Thalys for example.
The story is simple: TGV are designed to go really fast and bring you to your destination in under 3 hours. Everything else was secondary, the seating is relatively cramped, power outlets were introduced comparatively late, the restaurant car was always a stand-up bar/snack shop, etc.
By contrast, Swiss and German trains are still relatively slow (with a few exception like the Frankfurt-Cologne link opened with much fanfare … in 2002!)