Why do political parties try to avoid contested conventions?

-a candidate from a split party typically doesn't win the presidency

-a contested convention doesn't create momentum that a candidate needs to oppose the other party

Explanation:

The conventions are the elections of the pre-candidates of the diverse political parties in the united states are often used to promote their own candidate to gain mometum towards the actual election, candidates that have competition within their own political party often donot have the same exposure and build enough momentum to beat the candidate of the opposite party that didn´t have a strong contender in the conventions.

it was bribing i think i might be wrong though