But you shouldn't ask yourself why it isn't possible. The question is why it's not successful, or why there's no demand. America is satisfied by foreign alternatives. We don't want secure devices, we want cheap and simple devices that come in pretty boxes with the labels we like. Roomba et. al wins because it caters to the lowest-common-denominator, the basest American that most shoppers embody.
And America, collectively, cannot care. You won't see a law demanding software transparency or firmware alternatives for domestic robots. We won't assemble them locally because our labor is too expensive, we won't manufacture the chips domestically because it's cheaper to import them. You won't see people owning USA-made Roombas for the same reason you don't meet people using a Purism phone instead of a Samsung/Apple handset; the market has spoken, and they are absolutely apathetic to anything but price.