“Thank you, Alexa.”
I teach my kids to say “please” and “thank you” to assistant apps like Alexa and Siri. I know as well as you do that these apps are not people and do not have feelings. They use some neural nets and branching algorithms to find a best response to given verbal input, and polite words like “please” are considered semantically null in the process of evaluating your request.
But that's not the point. Other than Google, companies have chosen to give these apps human names, and want us to speak to them like we would speak to people. If we are going to talk to these devices like they are people they are basically a training ground for how we talk to real people. If my kids are mean to Alexa they're learning that it's okay to also be mean to the wait staff at a restaurant, or the cashier at a grocery store, or their mother at the dinner table.
So I want my kids to be kind to the robots in our lives, not because the robots need it, but because the kids do. And this means that I also say “please” and “thank you” to robots, and always will.
I realize that some people will see this as an excellent demonstration of the slippery slope fallacy, and point out that people can tell the difference between a human and an electronic hockey puck in the living room. And I agree, you totally can. But what is the harm in being polite to things that don't require politeness? I'm content to err on the side of kindness, and to teach that “error” to my family.