Why did the Latin language collapse?

Seems so strange that the most powerful empire's language, which spread all the way to Scotland, Israel, and Asia Minor would just become extinct...
It would be like the English Language dying. Maybe it will...who knows.

But anyways, i will never understand how a language that had so much influence in the known world, which is the basis of so many other languages, could just DIE. Many other languages have died, but they are isolated pockets..know what i mean? So strange, and illogical, at least to my amateur mind.

Hi all !
My question is how different are the classical version of the latin language and the medieval one ? I know that medieval latin varies from country to country so I will specify that I'm talking about medieval latin in England ( Britain ).
I'm asking becouse I'm currently studying the english medieaval latin and I have never studied classical latin before. I know that medieval latin was derived from vulgar latin but I don't know much about it else from it was spread to the foreign provinces by the soldiers. I don't know how related is it to the true latin. Therefore with the knowledge of medieval latin will I be able to understand the language of the late Roman republic and empire or not ?
I'm looking for both dictionary and grammar and further explanations would help.