Why did Latin case endings largely disappear in Romance languages?

The Latin nominal case system largely disappeared in Romance languages because the language shifted from a "synthetic" structure, which relied on inflectional endings to indicate grammatical relationships, to an "analytic" structure, which relies on word order and prepositions.1

Several factors contributed to this transition:

• Phonological Changes: During the development of Vulgar Latin, a strengthening of stress accents led to the shortening and loss of unstressed final syllables. Because many Latin case endings were located at the ends of words, their phonetic erosion made them less distinct and eventually superfluous.2
• Syntactic Simplification: As the case system weakened, speakers increasingly used prepositions to clarify relationships between words (e.g., using ad regem instead of the dative regi to mean "to the king").2
• Word Order: With the loss of overt morphological markers, word order became the primary mechanism for distinguishing the subject from the object, leading to more rigid syntactic structures compared to the flexibility of Classical Latin.31

While most modern Romance languages have abandoned the case system, Romanian retains a two-case system where inflected articles distinguish between the nominative-accusative and the genitive-dative.34