I draw the following conclusions:
(1) Don't think of the Anglo-Saxons (Saxons, Angles, Fries, Jutes, maybe more) as classic tribes. Only a
tiny, highly specialized section of those populations was lured into Britain, because of their skills, mentality and reputation.
This limited number of professionals became housecarls in Britain.
(2) They were less contaminated by the Empire, less instructed in Roman tradition and law. Roman law stipulated
that "all men are equal before the law". So, for the east-British lords, they must have been very reliable (the lords
considered themselves more equal). The 'Saxons' (as Gildas called them) had a very different and very principled background.
(3) The wages the north Germans demanded must have been lower. Constantine III was elected 'emperor' partly
because the wages for the British legions were delayed, or considered too low, or even not paid at all. To avoid such disasters, the
Anglo-Saxons were spread and paid by local lords.
(4) What the east-British lords wanted, was a personal guard primarily to increase their power locally and
secondary to fight the raids. The idea was never to form a classic army. Anglo-Saxons were simply not trained to serve in
(5) They served as a security layer between the less skilled and lower ranking British military in the guards and
the upper class members. This was the occupation of a housecarl. They could also be used against the landless British commoners.
This was something the British military were reluctant to do.
This explains the very small number of Anglo-Saxons in Britain. The system of housecarls would be continued up to
the battle of Hastings (1066). One of the tasks of the housecarls was to train and lead a militia called the fyrd.
For more see: Wikipedia, housecarl