star trek - Why do Vulcans have pointed ears?

We see Vulcans have pointy ears.

Why did the writers choose to make them have unique ears and not eyes or noses?

Answer

From a behind the scenes perspective, prosthetic ears were easy to do, but also, Gene Roddenberry wanted a slightly satanic looking character. He's never explained why, but he liked the look. Most people don't realize that ears do move along with normal facial expressions, but they do -- however they move less than the nose or other facial features.

Remember, this kind of work was still new and they needed makeup they'd be able to apply every single day that would hold up throughout the day. Doing makeup like this for a movie was one thing, since movies are limited in production time. But in the mid 1960s, having a character that needed anything like prosthetic ears (or nose, or anything else) was a completely new idea, so the less that had to be applied every day for 8 or 9 months each year, the more manageable it would be.

When they saw The Cage, the network didn't like it and asked that they get rid of the female 2nd in command and the pointy-eared guy. (On the recording Inside Star Trek Roddenberry joked that when they said that, he married the female 2nd in command and promoted the Vulcan. He added that he considered doing it the other way around, but it just didn't work out well that way.)

From an in-universe perspective, the air on Vulcan is thinner than on Earth, and evolution led to a different shape and slightly larger ear to help catch sound -- look at ears on animals that need to hear for their survival, like deer who hear predators. Many such ears are pointed.