[benlivengood]

A potential distinction is entropy preservation. For password hashes you usually want to preserve as much entropy as possible although one could argue that beyond 256 bits of output it may not matter (only one-time pads would suffer from smaller output). KDFs on the other hand must output a correctly-sized key for a particular cipher and so have further constraints on output choices (and potentially avoiding weak keys, e.g. for elliptic curve point generation).