The Great Vowel Shift: when did it really end?

Vowels (and consonants) are constantly evolving. Writing tends to freeze a time period's speech patterns, like a fossil of a life form, but the language continues to evolve. There was a sound change in Spanish-Portuguese from terra -> tierra, fazenda -> hacienda etc. Changes are constantly happening. Why a particular artist in a particular time period made the stylistic choices he or she did is something I don't know.