Clarification: It's infecting the control station computers (which I believe are still Windows XP), not the UAVs themselves.
Unless you want to make the argument that it's far worse for the ground control systems to be continually reinfected, as they have access to the rest of the air-gapped private network as well.
Well, at least it's easier to axe a box in the room than to shoot down a rogue UAV across the world.
It's far less worse that the control stations are infected as opposed to the aircraft themselves. It's pretty easy to shift control stations for a UAV. It's not so easy to regain control of a malfunctioning UAV. So, far from irrelevant.
That said, I was merely clarifying a common misinterpretation people were getting from the article.