Google NGram Viewer (https://books.google.com/ngrams/) measures the frequency of words as a percentage of all words used in print at different times in history.  The measure relies on Google’s database of scanned printed matter.  I do not know how much this database is a representable sample.  Nonetheless, based on my own research the frequency seem correct.  For example, I argued in my book that demands for an Einheitsschule, a comprehensive school system that advanced students on merit, took a quantum leap during the First World War, and indeed, Ngram suggests that was true.

So what happened to virtue?  Over the course of the last two centuries, people have used words that connote virtue less and less.  Input these words into Ngram Viewer: dutiful, faithful, trustworthy, generous, respectful, polite, gracious, devoted, courteous, congenial, sincere, honest. Their frequency all goes down.  Some exceptions of virtues that go up are: responsible, selfless.

Note that this word stays the same: loyal.

Now compare what happens to words that imply rights, fairness, or lack of these qualities.  They all go up.  Some example: fairness, just, equality, rights, inequitable, discriminatory, objective. Some exceptions of words implying rights that go down: merit, deserved, liberty.

So what happened to virtue over the last two centuries?  NGram suggests that, while it hasn’t disappeared, people value it less.