I’m honestly surprised it hasn’t been more prevalent yet. I still get call centre type spam calls where you can hear all the background noise of the rest of the call centre.
I assume it's to make it seem like an actual call center rather than a scam. I recently got two phone scam attempts (credit card related) that sounded exactly like this.
I built a voice AI stack and background noise can be really helpful to a restaurant AI for example. Italian background music or cafe background is part of the brand. It’s not meant to make the caller believe this is not a bot but only to make the AI call on brand.