I like to think of that as the (very rare) exception, not the norm, and not only because of recent events and social media. Before social media as we now know it: there was the landline, and mail.
Part of the problem is that we are now far more "mobile" as a society. The folks I spent every day of the first ~15 years of my life with are scores of years into my past. I've not seen nor heard from them. Nor do I particularly miss them. They were important to the CHILD version of me but not to the "post college" version.
Your experiences change you as well as your interests. I'd not know what to TALK about with any of those people.
If you are fairly (geographically) mobile, this repeats each time you set up a "life" in another location, distant (2 hrs by plane or car) from a previous "life". (the 2 hr figure tends to represent a significant effort to revisit the previous life-location)
And, as time moves while you are "away", those people and experiences slip further into the past, where they lose their potency.
Ask yourself how many of your classmates' names you can recall, from memory...
I'm old enough that I know a fair number of dead people. Each time I come across another, there's little more than a <shrug> involved.
Expecting MY demise to be met any differently would be vanity!
When a relative of mine developed dementia, the family tried to contact some of her oldest friends, consulting a small traditional contact book that she had kept. IIRC one person that might have mattered most could not be contacted; people had simply lost touch.
Staying in contact with people is costly. I spent many years volunteering at an organization where I worked with and interacted with several "repeat" individuals ("staffing" at volunteer orgainzaations is usually very fluid). These were people I enjoyed helping and spending time with. Having "gone our separate ways", I have to make a point of phoning (no text, thankyouverymuch! the time and effort required to type a few keystrokes is hardly worth acknowledgement AS an "effort"!) these folks periodically -- just to touch bases.
And, one has to make a point of keeping track of what is going on in their lives, even though your interactions are sporadic -- to give some continuity to the interactions AND indicate that you actually CARE about how they are doing and aren't just going through the motions of phoning, periodically.