I’ve already addressed a narrower version of the same question: Nick Nicholas’ answer to In the traditional British public school system, why is (or was) it believed that knowledge of “the classics” was necessary?
In the Renaissance, when Roman and Greek literature were rediscovered, that literature was treated as the source and reference point of all culture. To know that literature was to be cultured. […]
And the point of a liberal arts education back then, as it was in Ancient Greece, was not to get you a job. You didn’t go to uni for that; you went out as an apprentice, and people looked down on you as a mechanical. The point of a liberal arts education was to be cultured. To appreciate good literature. To form good judgement. To have good character. […]
And everyone doing science or literature read Latin, because that’s what intellectuals wrote in. And because they now had access to the classics, they would try to speak it more like the Romans did, and less like the mediaeval clerks did. Doing science and reading Cicero were part of the same package. It was all part of being cultured.
In the 16th and 17th and 18th century, the English developed their own literature. Gradually more and more science was written outside of Latin. So you didn’t need just Latin to appreciate good literature or do science. But the public school system stuck with it, because their ancestors did, and because Classical literature was still felt to be awesome, and because old habits died hard. And because you didn’t get a public school education to get a job. You got one to be cultured. Besides, any job you were likely to get as an aristocrat would be tied up with being cultured anyway.
Things have changed. Riff-raff […] get to go to high school and university. And we need to keep getting a job in mind, because we are riff-raff and not cashed up members of the aristocracy. And the Classics are only one option among many, and hardly the most prestigious one even among the liberal arts.