I'm going to be pedantic here, but... Bellof raced in F1 in '84 and '85, but he didn't race at Le Mans in those years, his only LM start was '83 (ended in DNF from a blown engine). In '84 the Porsche works team boycotted Le Mans due to changes in fuel regulations, and in '85 Bellof was driving for Brun but for some reason he wasn't on the driving squad for Le Mans.
Aha, well spotted!
Watson did in 85 (plus a one of Mclaren F1 race), Cheever did in 87, Baldi in 84 and 85, Weidler and Raphanel in 89, Giacomelli, Lehto, Alliot, Herbert, Gachot, Johanson & Donnelly in 1990. Herbert and Gachot both drove fairly comprehensive f1 campaigns in 1991, and they won Le Mans, too!
One reason there have been fewer F1 drivers racing at Le Mans in recent history is because there are fewer F1 drivers int total, due to the pitiful number of teams left racing...
After '91 it became less common to do Le Mans plus F1, though still happened occasionally. I can't imagine it makes Bernie very happy - and that in turn makes me happy.