First Aid did not understand. He stood to one side, watching Carly make a last adjustment to the machine that was helping mitigate the pain Sparkplug was suffering. There was no need for such pain; Carly herself was testimony to the fact Cybertronian science could integrate with human biology to produce a better frame for humans.
"Why?" he blurted, when the slow, weak blip of the monitor on Sparkplug's heart started to fade further.
Carly looked at him, tears in her eyes, and shook her head. "He didn't want to lose who he was, by becoming something he saw as different."
"He accepted you and your choices, as well as those of his son." It made no logical sense, and yet First Aid knew he should not be adding to her burden, when she was grieving even as she tried to make Sparkplug's passing an easy one.
Spike looked up from where he was by the bed, head having been bent against his father's arm. His eyes and nose were red with crying. "Parents want their children to live forever. Dad loved you guys, but deep down, he is pure human. He never felt the pull we did. But you guys gave us a chance to live on, and that? He loved you for even more."
First Aid didn't think that had cleared up his confusion any more, but he was not going to add to the pain in this room by continuing to question. There was no reason to die of mechanical failure so short a time after creation, when other options existed, but it was apparently part of the human psyche to resist change.
He only wished such decisions to refuse aid did not cause such deep pain for those left behind.