The Shambles said:

Perhaps the meaning of German words are less prone to change so much as words in a language like English - that is shared between so many different cultures and spoken as a first language in so many countries?

In fact, English is the most plastic, chanbeable language among all known languages. As far as I know, there is no accepted reason. Ask any well educated Spanish, French, German, of Russian speaker if they can make sense of their language's national epics, then go look at Beowulf. Even the Canterbury Tales is much less accessable than if appears to be at first glance.