Why dont English people speak German? if the Anglo Saxons came from Germany?

They still do. However, neither Germans or English speak the Saxon language as both English and German have evolved and changed since. (Listen to a recording of "Beowulf" in old English - it doesn't sound much Modern English or Modern German- infact, look at a shakespeare play in it's original form, even though that's 'only' 500 years old, form and structure of sentences are different from modern English). There is also the fact that French was the language of the upper classes following the Norman invasion so English is a mix of French and German.