I think it's a mixture of things. He has no utility, a low AP rating, and there are better straight DPS types. Just a comparison to a few for example:
Rey - comparable basic attack damage, but Rey's special does almost 50% more damage. Pilot's special actually does less than his basic. She's also 28 points faster.
Greedo - 20% less damage on the basic, but with crits Greedo regularly shoots twice and doesn't have a bad shot at 3 or 4 shots. Especially if some one like Sid is his lead.
IG-86 - basic attack isn't much to talk about, but special does same damage as Pilot's basic and calls an assist. If 86 is in a droid team the assist more than likely has increased crit chance and power, and will refill all droids' turn meters on a crit. So you could wind up getting 2 more attacks out of it.
Geo Soldier - His special goes every other turn, hits really hard, and calls in an assist with 25% extra power.
If the Pilot's unique had a little more uummph to it, (more crit chance or more turn meter added) I think he would be used more.