Et Latine Conundrum
The Romans had been speaking Latin for a thousand years before the Church came to power in the Empire. Many of the "other" Romance languages developed simultaneously with the big ones. Latin didn't change because it was highly inflected, all languages change over time. Not every word can be changed according to all of those variables, some of them apply to nouns and others to verbs. That is NOT why Latin is used to classify species, we just needed a common language for it. Some modifications are even more complex than Latin with two extra cases and 3 extra tenses (times). So, complexity is not really why the language died. We can express ourselves much more efficiently. English achieves its range of expressions with new words and phrases, we can achieve most of this with just grammar, plus we can add new words and phrases. The language is too complex to spark wider interest, but complexity can't be the reason because the roman empire was much stronger and widely spr...