Answer: Congress did not want to lose the ability to appoint friends and political supporters to key positions in the government
Explanation:
In the 19th century there existed a "Spoils system" in the United States where the winners of the election would appoint friends and political supporters to key government jobs to thank them for their support.
This meant that there were key posts that were not going to people of merit but rather people who simply knew those in power. There were calls to make this illegal but successive Congresses did not do so because they enjoyed being able to put their friends and supporters in power.