Air traffic control doesn't look like a complicated job. If we're to believe all we see from television and Hollywood on the subject, it involves little more than staring at a radar screen, watching as planes cruise overhead, represented by little blips on the screen. Your main job is to remind them not to crash into each other as they're taking off or landing. As usual, fiction hasn't been all that accurate in representing the complexities of the task.
There is only so much a pilot can see from the air, even with all the technology in their planes. You're their eyes on the ground. You're informing them of weather, visibility issues, runway availability, hazards in the air and on the ground, and flight paths when required to do so. You're also required to monitor baggage distribution to make sure the right baggage goes with the right flight. The job involves long hours, and absolute concentration for every second of every shift.