The same reason why the fact that I'm worried enough sometimes (e.g., major lightning storms) to unplug various electronics does not mean I choose not to own such electronics in the first place: sometimes isn't all the time, and both the costs of potential vulnerability and the benefit of features (and thus the balance between those two things) can shift with context.

Though, in reality, I'm never actually that worried about my Google Home, I just recognize that this there are adequate existing hardware-based solutions that, should I be concerned at some time—which I can imagine being, though I haven't been—an adequate mitigation exists that doesn't involve not possessing the device.