Amines do not attack carboxylic acids

This is because the acid will quickly lose its proton:

Almost no nucleophile will attack a carboxylate anion. Organolithiums are one exception.

One way of forcing this reaction to take place is to use high heat - which dehydrates the salt:

I don't know the mechanism. It is also seen as a bad way of making amides - but I don't why.

And unlike alcohols, the reaction cannot be catalyzed by protonating the C=O, since any acid will preferentially produce an ammonium ion - which is obviously a poor nucleophile.