Password hashes and key derivation functions can be totally different - key derivation functions only need to be slow if they're intended for low-entropy input, while password hashes in no way need to maximize entropy (e.g. "bcrypt, then 128 zeroes" is a perfectly fine password hash, but I wouldn't want to use the result as e.g. an AES key.)
In practice, though, it's desirable for password hashes to maximize entropy, which makes them usable as key derivation functions; and the key derivation functions that you usually need take passwords as input.
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Password hashes and key derivation functions can be totally different - key derivation functions only need to be slow if they're intended for low-entropy input, while password hashes in no way need to maximize entropy (e.g. "bcrypt, then 128 zeroes" is a perfectly fine password hash, but I wouldn't want to use the result as e.g. an AES key.)
In practice, though, it's desirable for password hashes to maximize entropy, which makes them usable as key derivation functions; and the key derivation functions that you usually need take passwords as input.