In October 2020, Chileans were asked to vote in a referendum on whether the country should write a new constitution; eighty percent voted in favor. Nevertheless, when parties on the Yes side formed candidate lists for the constituent assembly, they displayed extreme fragmentation. This study is meant to explain how this apparent unity dissolved into disunity. It hypothesizes that the party fragmentation process is not recent but rather ongoing since the last decade. I analyzed this fragmentation process using data from Chile's electoral agency. I calculated Laakso & Taagepera's index of effective number of political parties in the elections for the Chamber of Deputies as a marker of fragmentation over a longer period. Next, I compared the evolution of Chile's party system between 1989 and 2017 to the 2021 election of representatives for the constitutional convention analyzing possible significant differences in fragmentation distinct to the 2021 election. Two main results were obtained. First, political fragmentation was a process already ongoing by 2013. Second, even more fragmentation took place after the 2015 voting reform. This phenomenon was even more marked for the 2021 Constitutional Conventional elections than for the 2017 Chamber of Deputies, even under highly similar voting systems. I offer an explanation of these results following Cox's (1997) work on strategic voting and entry from non-partisan groups into political parties and lists. The lack of electoral history for this type of election and district sizes made strategic voting difficult, impeding to reduce the number of candidates and lists. At the same time, the erosion of traditional party brands, and the lower entry costs, made the entry of new actors easier without needing to participate in existing parties.