You are right KJV isn't easy understandable ... the NWT is easy to read
I don't even speak English natively and can read KJV. I guess it just isn't more difficult than reading in foreign language in general.
Update: Samuel Johnson's dictionary helps with word definitions from 18th century. Noah Webster's dictionary is good too.
In the case of NWT I think the bias matters because JWs deviate fatally from Christian orthodoxy.