I thought it was Balestre that brought in the 3.5 rules, not Bernie, and had been trying for years.
To my knowledge, Berrnie was behind it and he was clever enough to get Balestre so far to cooperate and take the lead in the matter. Bernie knew all too well that if sportscars disappeared that there would be fingerpointing who was resposible for that. He definitely wanted it to happen to see newcomers in sportscars with suitable 3.5 liter engines coming to F1 instead since they had a suitable engine. He only got Peugeot.
Bernie was also behind the move to get the TV rights of sports car racing (Gp C) in his hands and then market it. Before that, Brian Kreisky and his company Videovision were allowed to cover the Gp C races and these reports were shpwn on Sky Channel's International Motor Sport. That program and these reports created a lot of interest with the audience for Gp C racing. When Videovision had to deal with Ecclestone, the reports ended and popularity of Gp C other then Le Mans went down.
Ecclestone then came up with the idea to market shorter sprint races that could be easier to sell for live TV reports but the original Gp C rules had lead to cars that were not down and outright sprint cars so a change to lighter, more agile cars, more suitable for sprint style racing came handy. And that pretty much spelled the end for anything longer than 500 km and thus endurance racing as we knew in from the original Gp C. It was suggested that F1 equipment could come handy in that too. But the real aim of Bernie was the opposite. F1 did not need to bolster the Sportscar fields but sportscars first had to be much closer to F1 specifications and then killed off so the factories could make the step to F1 easier.
from 1982 till 1990 you had the Groep C(lassic)
From 1991 till 1993 there was the Group C(atastrophic)
Courtesy the greed of Bernie Ecclestone and the lack of intelligence of Balestre to underestimate Bernie's real interests and focus.
Henri