It's genuinely a very similar problem. The max round trip latency before polite humans start having trouble talking over each other has been well studied since the origins of the Bell Telephone system. IIRC we really like it to be under about 300ms.

AI has processing delay even if run locally. In telephony the delays are more speed-of-light dictated. But the impact on human interactive conversation is the same.

Is it because you've never used copper pair telephone networks and only have used digital or cellular networks?

POTS is magical if you get end to end. Which I don't think is really a thing anymore. The last time I made a copper to copper call on POTS was in 2015! At&t was charging nearly $40 for that analog line per month so I shut it off. My VoIP line with long distance and international calling (the pots didn't) is $20/month with two phone numbers. And its routed through a PBX I control.