Easy, back in the day all we had was phone call for instant communication, so not much to compare to.
Also, you didn’t call a person, you called a house or place of work. This meant it was used more sparingly (need to keep the line open/share with the rest of the house) and if you were away, then that phone call couldn’t bother you. This also meant people were used to not being able to reach who they wanted to talk to, so if you felt like letting the answering machine get it, no one would think anything of it. You were either on the phone or present in the moment, not trying to talk with a number of people who don’t know each other.
Now everyone has a phone at their hip. You can call someone and if that someone sends it to voicemail, you know they did and it can become a point of drama depending on the circumstance. Now I can be in the middle of text conversations with a half dozen people across half the world and so when my phone unexpectedly rings then I wonder who is this asshole who thinks they deserve my full attention over these other folks, even though the other person has no way of knowing about those conversations. We are expected to juggle concurrent conversations and a phone call derails that.
This creates a generational disconnect. Like when my phone rings unexpectedly at work, it’s 95% this one colleague in his 70s who is nice enough, but it instinctively feels rude because I feel like I need to answer. From his perspective, if I just don’t answer that’s fine and that’s the etiquette he was used to, try to call and no biggie if it doesn’t connect.
Going the other way, I know someone dealing with a person in their 80s over urgent important stuff and that person just will be utterly unreachable so much of the time. For them, there’s no such thing as “urgent enough to need immediate attention” because that was just not possible for them and society developed around the norm of folks just not being available as much.