Why did spoken Latin gradually diverge from Classical Latin?

Spoken Latin diverged from Classical Latin primarily because it was a living, evolving language used by diverse populations across the Roman Empire, whereas Classical Latin was a standardized, written norm.12

This divergence occurred through several key processes:

• Phonological Changes: A strengthening of stress accents led to the shortening and loss of unaccented syllables. Additionally, the system of long and short vowels—essential to Classical prosody—was lost, resulting in qualitative changes to the language's rhythm.32
• Grammatical Simplification: Speakers increasingly favored analytic constructions over the complex synthetic forms of Classical Latin. For example, prepositions were used to replace case endings, making the language simpler and more rationalized.3
• Lexical Shifts: Popular speech frequently rejected sober Classical vocabulary in favor of more colorful, expressive terms, such as diminutives and derivatives.3
• Regional Variation: As administrative unity collapsed, regional accents and usage patterns—which may have existed throughout the imperial period—became more pronounced, eventually forming the basis for the distinct Romance languages.12

While Classical Latin remained a uniform standard for scholarship and religion, the spoken language continued to evolve naturally, eventually becoming perceptibly distinct by the 8th or 9th century.12