Why did Brits adopt foreign Germanic language instead of continuing speaking native Celtic?

[Sikeliot]

Interesting thing: English has almost none Celtic Influence other than Western Dialects. Much more Latin & French.

Seem like Celts had no power at all.

English does have some grammatical features in common with Celtic languages and not with the other Germanic languages.

Anyway to answer the question, it is because speaking Celtic, rather than Anglo-Saxon, resulted in social ostracization, and it became necessary for the Celts to learn English if they wanted to prosper.

[Livin]

For the same reason why indoeuropean speakers imposed the natives pelasgians,minoans etc pre-greek populations to talk the GREEK!!!

[Alcuin52]

1. The wealthiest, ruling British elites probably spoke Latin

2. Britain, being a 'frontier province', undoubtedly retained the pre-Roman concept of tribes (hence why Britons' kingdoms arose so quickly after Rome's withdrawal)

3. Sub-Roman Britain was, almost certainly, in many regions, a chaotic land-grab between the less Romanised rural Britons, Romano-Britons leaving the decaying cities that they didn't have the skills or knowledge to maintain (probably including retired legionaries and imperial military men who didn't return to the continent), invading Scots (Irish) and Picts, and ultimately the Angles, Saxons, Jutes, etc who first arrived in Britain as hired mercenaries of the aforementioned groups

All of this paints a picture of a Britain that did not stand a chance of putting up a unified defence, ironically the same problem that had allowed the Romans to conquer the island in the first place, and this is evidenced by the writings of the likes of Gildas

Let's not forget, though, that Common Brittonic (and its later derivatives) was spoken in Northern 'England' for several centuries after the first Angles and Saxons settled in Britain, and it was in this part of the world that most of the famous 'Welsh' heroes lived, ruled and wrote. Aneirin, Taliesin, the 13 Treasures of Britain... none from the region we now know as Wales, which was a less Romanised and more lawless region than 'England'. The places we know today as Cumbria and Yorkshire were the birthplace of modern Welsh culture.