Why is "poison" in English pronounced so differently from French "poison"?

Why is poison in English pronounced so astonishingly differently than the French pronunciation of poison? Considering that they have exactly the same origin. Is it just randomness or is it on purpose just to not sound "like the French"?

From Old French poison, from Latin pōtio, pōtiōnis, from pōtō.

It has to do with when the sound shift occurred. The change to /wa/ in what is now Modern French (which is a langue d’oïl not a langue d’oc like Provençal) happened after the Norman Invasion. From Wikipedia:

In some contexts, /oi/ became /e/, still written oi in Modern French. During the early Old French period this sound was pronounced as the writing suggests, as /oi/ with stress on the front vowel: /ói/. The stress later shifted to the end position, /oí/, before becoming /oé/. This sound developed variously in different varieties of Oïl language – most of the surviving languages maintain a pronunciation as /we/ – but literary French adopted a dialectal phonology /wa/. The doublet of français and François in modern French orthography demonstrates this mix of dialectal features.

Also, even though Norman French was also a langue d’oïl (albeit with other influences), do not assume it underwent the same sound shifts as Parisian French.

Because English borrowed the word from an older stage of French, before /oi/ started being pronounced [wa], and before final nasal consonants merged completely into their preceding vowels, giving nasal vowels.

The modern English pronunciation is actually quite close to how it would have sounded in Old French, except Old French would have had the stress on the final syllable, rather than the first.