>>6364
The psychology of fear is well beyond a basic psychology degree. There are a few things about these types of creature drawings that are fairly apparent though.

As already mentioned, uncanny valley stuff and disease/injury revulsion is a big part. This effect also applies when something has a part that looks human, but it isn't a human. Humans are also wired to be afraid of stuff that is angular or sharp looking, including physical shapes and movements.

We also fear stuff that is unfamiliar, which obviously applies to pretty much all monster drawings, but is more potent when the thing does not look "natural". This is a bit more difficult to exactly define, but we get used to how biological creatures "should" look based on our experiences, stuff that doesn't fit in causes more fear. As an add on to this, we also fear stuff that doesn't have function we think it should have, e.g. no eyelids with eyes, eye sockets but no eyes, teeth but no lips. We are also afraid of stuff that has exagerated body parts that can be dangerous like mouths, claws, or hands.

There is a shit ton of stuff I didn't touch on or just don't know, but my point is that there is a lot that goes into defining why scary stuff is scary.