Well, the Bloc didn’t exist back then. Trudeau was actually quite liked in Quebec originally. I wasn’t there at the time, but here’s how I would explain it (and I may be somewhat off).
Until the sixties, francophones were still a disadvantaged group in Quebec, despite being the majority. The Liberals were elected in 1960 and Lesage’s government started to reverse this situation. This work was continued by the rather nationalistic Union Nationale government of Daniel Johnson. At around the same, Pierre Trudeau erupted on the federal political scene. He wasn’t a Quebec nationalist – far from it – but he was still a francophone Quebecer who had succeeded in federal politics, becoming leader of the federal Liberals just a few years after becoming active in the party. He also had the dream of making the French language equal to English in Canada. This was music to the ears of francophones inside (and outside of) Quebec: after decades of being subordinate to anglophones, of having to speak English with bosses even in Quebec, they were being told that they weren’t second class citizens anymore, they were an important culture of what was to become a multicultural Canada, their language was to be made an official language equal to English, and even the anglophones were supportive of this.
It’s not surprising that francophone Quebecers voted en masse for Trudeau at the time. Francophones outside of Quebec probably still hold Trudeau in high esteem today, but during the following years, the political winds changed in Quebec. A number of Quebecers came to believe that the Trudeau ideology was a unrealistic dream, and some of them decided that independence was the only way for the province to fulfill its potential. The Parti Québécois was elected in 1976. But at the same time, who was there to vote for at the federal level? Some voted for the Rhino Party, founded by separatist doctor and writer Jacques Ferron. (Anecdote time: one of my French teachers in cégep was a scholar on Ferron and a Rhino candidate from that time. If I remember correctly what he told me, the Rhinos were mostly intended as a parody of the Liberals: politicians who lie and make empty promises, but who admit it!) The others mostly voted for the Liberals, since the Conservatives were at the time traditionally unpopular in Quebec, and because Trudeau, for all his faults, still clearly supported francophones.
This ended in 1984, about the same time Trudeau stepped down from power. The Conservatives had selected a new leader, Brian Mulroney, who promised constitutional reforms to allow Quebec to find a place in Canada and sign the Constitution, which was repatriated by Trudeau with the approval of all provinces except Quebec. I believe Mulroney came close to causing a schism in the Parti Québécois. Some former separatists, like Lucien Bouchard, became federalists and joined his team. René Lévesque spoke of the beau risque of giving Mulroney and renewed federalism a chance and was forced out of the leadership of his party by the hard-liners. (Still, the PQ selected another soft nationalist, Pierre Marc Johnson, who I’m not sure is even a separatist today, as their new leader.)
Of course, what happened is that Lévesque’s beau risque failed. He wasn’t there to see it anymore, but Bouchard was, and we know the rest. My point is that Trudeau couldn’t have been elected in Quebec after 1984, and he certainly wouldn’t be today, with the Bloc as a proven alternative.