Actually it is allowed at TLM.
Mediator Dei clearly allows it.
It might help to remember that in 1947, the Mass was in Latin, and precious few people were fluent in Latin. It was not taught as a spoken language for the vast majority of people who studied Latin, but rather as a translated language; with enough years of it one might be able to read in Latin.
Professor Waldo Sweet became an assistant professor at the University of Michigan and in 1957 produced
Latin, A Structural Approach.
I started high school in 1960 with the standard translation method. 2 years later I transferred high schools, and found myself in a Junior year Latin class with the Sweet method = as a spoken language - and I was so far in over my head I was drowning. However, Homeric Greek class was taught as read/translate, and I did fine.
In college seminary I was back to reading and translating - no one spoke in Latin.
At the same time, there were missals available with Latin on one side and English on the other, and I may have been the only child in my grade school class who had one; they were expensive, and most people did not buy one.
Thus people were at the same extreme disadvantage they had been at for centuries after the Roman empire had lost its sway; they attended Mass in a foreign language, with no means of understanding it, and pious devotions, primarily the rosary, took the place of participating in the Mass as it had been in the languages of the people - Aramaic, Greek (which was widely spoken and in which the Gospels and Epistles were either written, or soon translated into), and following the Roman conquests and the change to Latin as the “second” language of many peoples.
The Mass was never meant to be a “duty” to attend by simply sitting/kneeling/standing without any understanding of what was going on; the rosary provided a means of doing something of a religious nature while the priest said the Mass in a foreign language.
Pope Pius 12th spoke to a centuries old tradition. Pope Paul 6th spoke to what the Mass was about, and by then it was clear to a whole lot of people that the Mass was not something that was simply to be endured while one did something else.
There are now missals available at low cost (and most often provided by the parish) in the OF - whether one prays along with the priest better by listening or by reading, one is able to participate along with the priest in praying the Mass.
And the same is available to those who prefer to attend the Ef - although whether the parish provides missals or the individual buys them, the point is the same - participating and praying along with the priest.