why do amines act as a base but amides do not?

In amine group, the lone pair of electrons on the nitrogen atom is available to accept a proton (hydrogen ion). Therefore, amine can act as a base.

In amide group, the lone pair of electrons on the nitrogen atom undergoes resonance as shown below. This makes the lone pair of electrons on the nitrogen atom much less available to accept a proton. Therefore, the basic strength of amide group is very low.