What factors led to the convention replacing the caucus as a widely used nominating method?

I believe the answer is: we want our voters to educate themselves without outside opinions conflicting with our own beliefs that affect our voting choices

In a caucus, the representatives of each party for the presidential election is appointed by the voters, not the party. This make a lot of them appoint only someone that they know directly (such as friends and relatives) . Due to the complication of this method, the process changed into convention, where the right to choose the representatives for presidential candidates belong to the party.

the answer should be:

their party has more members.

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