GPT3.5-level models are now insanely cheap: $1 buys you something like a Moby Dick's worth of text. STT and TTS models are getting cheaper too. I'm guessing that they are betting usage over the lifetime of the device (maybe 2 years tops?) amortizes out to a decent margin without a subscription.

It's also a lot easier to stomach a beautiful shiny teenage engineering toy that doesn't do much if you don't have to pay every month.