Why does a Galilean telescope have narrower field of view than an Keplerian telescope with the same size lenses?

This is due to the eye piece consisting of a diverging lens

Explanation:

Galilean telescope have a narrower field of view than an Keplerian telescope with the same size lenses due to the eye piece consisting of a diverging lens while the Keplerian telescope eye piece has a converging lens.

The presence of a converging lens in the Keplerian telescope enables it to have a larger angle difference while the Galilean telescope diverging lens enables it to have a smaller angle difference which explains its narrow field of view.