I see two possible reasons for your situation. One is that the company is turning to contractors to fill in gaps in their knowledge/experience, which is why everyone else has no clue how to tackle these tasks and why they get assigned the easy ones.
The other possibility is that the senior devs are gaming the metrics, letting the employees knock out easy tasks while the contractor is stuck with untangling the knots of the more intractable tasks.
"Remain wary of the frailty of men. Their wills are weak, minds young. Were it not for fear, death would go unlamented."
"Seek the old blood."
"Let us pray, let us wish... to partake in communion. Let us partake in communion... and feast upon the old blood. Our thirst for blood satiates us, soothes our fears."
"Seek the old blood."
"But beware the frailty of men. Their wills are weak, minds young. The foul beasts will dangle nectar and lure the meek into the depths."
"Remain wary of the frailty of men..."