Explosive Bolt and Projectile Damage

Is there a reason that explosive bolt doesn't seem to benefit from increases to projectile damage? If I allocate a +X% to projectile damage node on the passive skill tree, all of my crossbow skills reflect the increased damage except that one.

It does, but I think it’s because it’s one of those skills with 2 part damage.
The initial projectile itself which does minuscule damage is where the +projectile damage is applied.
Then the actual explosion where the majority of the damage is, doesn’t get the +projectile damage because it doesn’t count as a projectile.