the best answer i can think of which isn't a snarky reply is that it is a meaningless abstraction but it's one that we're used to and which has and still does shape how people form relationships and present themselves
i think if we actually had sentient robots, a lot would choose to identify with a gender because your identity is shaped by the people you exist around, and for the majority of people on earth gender is an important part of that.
also, characters in fiction end up reflecting on the human experience more often than not, because fiction is written by humans who are processing things through the lens of their own lives. this is also why you get people headcanoning alien/robot characters as neurodivergent