> Well, that's because they're really languages and not dialects!
Indeed they are not strictly dialects of Italian, which followed its own evolution alongside them. I think most of them could still be explained as dialects of Latin, who underwent major "niche differentiation" in the immediate aftermath of the fall of Rome and the rise of barbaric kingdoms.
> [Italian] was mostly a written/literary language before that.
This is a bit of an exaggeration. Clearly, even before the early modern era "Italians" could understand each other. Dante (from Florence) lived in Genoa and Ravenna, and had no need for an interpreter from what we can gather. Ditto the many "Renaissance men" who toured around Italy (Leonardo: Florence->Milan; Raphael and Michelangelo: Florence->Rome; Galileo:Pisa->Padua). This level of interconnection becomes really hard to explain without a high degree of mutual intelligibility.
Dante is a poor example for language proficiency, as he was educated / traveled/ well read. The common person would have a much different lived experience
I have colleagues in India. It's a diverse mesh of regions that vary in about every way. Was explained people grow up with 3 languages, their regional language, a neighboring region's language, a more general language, & then educated folk are taught English. Then in school they were still taking classes for other romantic languages. At an Indian restaurant with one colleague I noticed they would mostly rely on hand gestures. One factor here is that there may often be a language barrier
I've also interacted a bit with Senegalese, which has Wolof as the primary language, then French taught in schools. Many only know Wolof (with French influence weaved in). & the well educated learn to speak English, & how to maintain more European French accent
Indeed they are not strictly dialects of Italian, which followed its own evolution alongside them. I think most of them could still be explained as dialects of Latin, who underwent major "niche differentiation" in the immediate aftermath of the fall of Rome and the rise of barbaric kingdoms.
> [Italian] was mostly a written/literary language before that.
This is a bit of an exaggeration. Clearly, even before the early modern era "Italians" could understand each other. Dante (from Florence) lived in Genoa and Ravenna, and had no need for an interpreter from what we can gather. Ditto the many "Renaissance men" who toured around Italy (Leonardo: Florence->Milan; Raphael and Michelangelo: Florence->Rome; Galileo:Pisa->Padua). This level of interconnection becomes really hard to explain without a high degree of mutual intelligibility.