Now, why is that? Why are they only two? For one thing, they escaped getting burned during the dire conditions at the middle of the 6th century.
Now, why did the Angles and Saxons arrive? Why did they want to leave a vast continental area devoid of enemies just to go to Britain to fight with the technologically superior Britons? Well, it was real bad back home. In fact, the islands the Angels (Frisians) lived on were unlivable and the rest of Germany where the Saxons lived was getting very nasty ~ crop failures were common.
Still, you will note that BOTH documents were written by guys on islands which were not affected as much by the change in climate that was driving people out of the Continent.
Yes, islands ~ Britain is an Island. Scota is an island (and would one day in the future be called Ireland).
As you recall, I noted that folks on peripheral island areas did much better than people on the continents.
A similar phenomenon happened on the East Coast of Eur-Asia. Koreans departed from the Korean peninsula circa 560 and arrived in Japan where they took over and founded the present dynasty. These people were escaping bad weather, a devastated economy, and going to a place where food was still growing.
So, come up with all those other books published in Germany in the 500s ~
You've posited a theory, full of assumptions and question marks. It is not up to me to search out data for you. Every time I have pointed out evidence that contradicts your pronouncements on this thread, you have chosen to ignore it and shift your argument.
The facts are these: There were lots of things written on the continent during the 500s. No one, to my knowledge, speaks of the event you posit occurred in the 540's. I could posit that space aliens came down and flew the pyramids over Constantanople, and you could not prove it didn't happen. You can only show evidence to prove a positive.
So show your positive proof of a massive European depopulation due to a fimbulwinter.