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.
> english happens to be spoken all over the globe due to a big goofy empire that went places
Why do you think Latin was popular?
Well, it wasn't universally popular is my point.
Latin was the language for education and science waaaay beyond ex Roman Empire. Pretty much whole christian europe used Latin in medieval age and beyond.
Christian Europe waited until the XIII-XIV to get most of its latin inheritance in latin. Before that it was either greek or arabic.