I was wondering if it's an evolutionary advantage to have many sensory systems in a small place of the body, the head. This applies to mammals, reptiles, synapsid, dinosaurs... and many more.
- The distance to the brain is short and thus smaller time delay to respond faster to the outside world,have more reflexes, hunt faster prey and fight more accurately.
- The short distance makes the "wire" (signal carrying) shorter and thus less vulnerable to be cut from a injury, because for a organism losing an eye reduces possibilities of survival dramatically.
- In humans at least the head is the upper part, then vision organs see more with less obstacles such as vegetation or terrain irregularities, or anything that obstacles vision, normally higher means seeing more things. This I'm not sure applies so strongly to smell. To taste, certainly not. To hearing, possibly a little, thought nor much as vision.
We evolved from a common ancestor that was like that but that doesn't explain why it's not common to get out of that coincidence.