Conventions were run by the political insider's.
To win the nomination, the nominee had to make countless deals to pay off the Party leaders in the States.
Lincoln was greatly vexed by the promises made by his campaign leaders that he had to fulfill after he was elected President.
By 1912, twelve states either selected delegates in primaries, used a preferential primary, or both. By 1920 there were 20 states with primaries, but some went back, and from 1936 to 1968, 12 states used them.
Thanks for that info. Made me check up on that.