Why do political parties switch to national conventions to nominate presidential candidates

To include more people in the process.

The national convention is intended to vote for winners from

the primary caucuses and select a presidential candidate. the movement is to

encourage people who considered themselves as partisans to participate in their.

party's presidential selection process.

The purpose of the National Conventions besides nominating the presidential and vice-presidential candidates is to facilitate the adoption of a comprehensive goals and principles platform to unify the party by including more people and laying more political power on the citizens.