Because latin was common only for part of one continent where he happened to be and not to the rest of the world while english happens to be spoken all over the globe due to a big goofy empire that went places.
However, let's keep out the culture wars from a post mainly about plants.
If in 17 hundreds you wanted to choose a language that could be deciphered, say, also in China, Latin was a much better choice than any native language in various vicinity.
In XVIII there was no language that could be universal was my point and latin was known mainly through its derivatives.