Why is the first base mans glove different?

The main objective of the first baseman is to catch the ball. A larger glove or mitt, would be an advantage. Infielders need to catch the ball and quickly transfer the Baseball from glove to hand, to make a throw. A smaller glove has an advantage.

The infielder also needs to have a feel for the ball to help grab the ball or handle tough ground balls. The first baseman's glove or mitt has extra padding and leather to protect the hand from hard throws.