> the Second Vatican Council decided Mass should be said in the vernacular
It didn't actually.
See Sacrosanctum Concilium: https://www.vatican.va/archive/hist_councils/ii_vatican_coun...
Vatican II opened the way for use of vernacular in the Mass while also directing "use of the Latin language is to be preserved in the Latin rites".
In practice, after the overhaul of the Latin rites was completed and promulgated (published) in 1969, four years after the council ended in '65, the Latin language itself was dropped almost everywhere all at once and only translations were used. Many people rejoiced at that, some did not, but the vast majority of bishops, priests and laity alike, conservatives and liberals across the full spectrum, probably 99.999%, went ahead full throttle with Mass and all the sacraments in the vernacular.
There were hold-out contingents like the SSPX, led by Archbishop Marcel Lefebvre, who stuck with the all Latin rites per the last round of small reforms in 1962, the same as used for the celebration of Mass, etc. during the whole time of the council from 1962-65.
It was over the next 40 years that discontent with the reforms of 1969, and their fallout, began to grow. There was increasing awareness that it wasn't just a switch from Latin to vernacular — the '69 reforms were "cut from whole cloth", outright replacing the traditional rites with syntheses of a commission of scholars. Long story short, many Catholics, some born before '69 and many born after (myself included), desire a return, and have implemented a return, to the traditional form of the Latin rites. Pope Benedict XVI gave it his blessing. But then Pope Francis was not a fan, believing it to be a retrograde movement that causes more harm than good and a kind of "saying no" to the Holy Spirit. It's hard to find middle ground on this matter, to be quite honest.