Vaggagini says somewhere "Three tendencies were manifested: some wanted no concessions to the vernacular; some wanted permission to say everything in the vernacular for all who wanted it; some wanted to maintain the basic principle of Latin, but also to open the door noticeably to the vernacular tongue." (The text of Sacrosanctum Concilium at para 54 actually reflects this stage of understanding very closely.) The last group, he said, were by far the largest. So, if you put that together, you clearly find that the overwhelming majority of the Council Fathers wanted at least to preserve a basically Latin Liturgy. And thought they were voting for this!
All but four bishops voted finally for the draft text: and those four lonely dissenters did not include Archbishop Lefebvre. He and his friends were happy with what they had voted for; with what they imagined they would get.
So how did we end up with the practical disappearance of Latin in less than a decade? And a radical deformation of the Roman Rite?
A friend once left a comment advancing the hypothesis that the Council, if anything, attempted to put the brakes on the radical slide into innovation which had been begun, on his own initiative, by Venerable Pius XII. I think there could be something in that. How about this as a summary of a possible narrative:
Over the decades, an international network of professional Liturgical Experts had grown up who were mostly not particularly marked by precise or original scholarship but maintained a close network of meetings, conferences, and journals. After the Council, they soon came to dominate the Diocesan Liturgical Committees which the Bishops set up, and then the liturgical bureaucracies created by the Episcopal Conferences. Bishops felt that they themselves didn't really know about Liturgy and were glad to be able to leave it to The Experts.
You remember the hoohaa that started up when Joseph Ratzinger began to write about Liturgy: "But he's not an expert in Liturgy". They meant: he's not one of us and he hasn't participated in our conferences and our journals and our international common agendas.