Why did president john adams make the "midnight appointments"

The correct answer is - jobs in manufacturing and trade.

Most of the immigrants that migrated to the United States were doing it because of the prospect of having a job in the industrial facilities that were become more and more and bigger and bigger in the quickly growing economy of the United States. So people from lots of parts of the world were trying to get to the United States, some found it easier, some were not allowed or were allowed in limited number (the Chinese for example were allowed only 5,000 people per year)