A lot of FUD (fear, uncertainty, doubt) in this thread. I'm a software engineer working on smart devices and smart phones.
Your phone isn't constantly listening to you. It would absolutely destroy the battery. Since Apple is closed source I can't exactly tell (other than having packet sniffed the traffic from their devices), but on Android you can read the Linux kernel yourself. It's modified to put the device to memory suspend mode (the CPU is literally unpowered) fairly quickly. You know how your phone lasts more than a day? That's because the CPU isn't running until you press a button to wake the screen (hardware interrupt request). Not to mention watching the packets flow from these devices only shows voice traffic to servers when the Google Now / Siri application is in the forefront. Otherwise you might get 8 hours of battery life, depending on the device.
Same thing goes with Google Home or Amazon Alexa devices even though they're plugged in. There's a keyword spotting process to wake the device and start sending the voice packets to their servers in order to figure out what you're saying. The microphone is picking up everything you're saying, yes. But the transmission isn't sent until that keyword matches something (a mathematical hash) the device is set to listen to. A company named esoftthings (out of France) does a lot of this engineering and it's fairly complex. Multiple keywords increases the complexity. Sending streams of voice data is not happening (currently..ahem) on these devices.
Now to why you're seeing ads for things you are talking about
: your data is available to these companies, particularly Google, and they're really good
at matching things you might be interested in. Scary good. Should-be-illegal good. The things you're getting as suggestions are based on a ridiculous amount of machine learning done over years and billions of people to know that you're likely to want to listen to some band. Or, in the case of Facebook, a particular news article (no matter how much truth is in it or how much it creates echo chambers) or personal post is likely to keep you on their platform
. The longer you're on that page / in that app, the more money they can make off selling your data.
The average person is worth about $15 a month to Google. $13 to Facebook. They're good at justifying that cost. Your devices aren't listening to you. They just have enough data to show you what they think you want to see.
Personally, I don't have any "smart devices" in my house. And I never use voice commands because I don't like talking to a phone. I Ad block, pi hole
(fantastic and highly recommended), use my smart phone less than most less-technically-inclined people. If you're really worried about all of this, then I suggest not logging into a Google account while browsing the internet, clearing cookies when you close your browser, check out DuckDuckGo.com instead of Google, disabling all Google tracking preferences on your smartphone...
I guess there's a reason I prefer to spend my free time in my garage. But Google already knows that.