It's what we all grew up with if you're older than about 50. The phone rings, you answer it. It's a habit. Even caller id wasn't really common, and it cost extra.

OTOH I'm in that age group. I dropped my landline a long time ago, and I never answer calls on my mobile unless the caller is in my address book. I don't have voice mail either. The habit of answering the phone was not hard to stop, there was a bit of FOMO (if you can call it that) for a while, but every time I answered such a call it was a scammer or a survey or some other nonsense so that's pretty much gone away.

Maybe for those that are truly elderly it's just something to break up the boredom of sitting at home.