I find this hard to understand especially because Latin itself has little to do with the origins of Christianity and was originally adopted precisely to make the liturgy understandable to western Romans. So, once people didn't understand it anymore, why did it linger until about 50 years ago?
I wrote in the past an answer on the reasons for keeping the latin language after the Council of Trent
The policy was not uniform nor enforced everywhere and everytime: in his De Expositione Missae the deacon Florus of Lyon (IX century) spoke about priests that celebrate part of the Mass in 'vulgari sermone', and you could find other more recents examples as this.