I sympathize with questioning but this is pretty harsh. The explanation is fairly simple. “It” is how we refer to most inanimate objects and “subhuman” creatures in the English language. Debates on how appropriate it is to be addressed in this way or desire to be addressed in this way aside, it’s certainly not random or a stretch to imagine why some might be uneasy with the idea if they feel it somehow associates the person with the aforementioned categories.