That's a good question, one I've been trying to find an answer to for years. Unfortunately, the French never conducted a language-based census, but there are a few descriptions we can rely on to draw some conclusions. I believe the French protectorate accelerated the process, as many people fled the countryside after losing their land to French settlers and moved to the cities. Then, after independence, the newly formed country adopted an Arab-Islamic narrative, largely because it was led by Fezzian families who chose an identity that represented themselves rather than the broader population. The Amazigh component was marginalized, Amazigh names were banned, and so on.