I'm the same age as you and I don't think it was "very rare" - my parents divorced when I was 6, and I definitely wasn't the only one in the class although I think I was a minority. Maybe you didn't know the marital status of every child's parents? I only know the ones whose houses I went to play at.
What I did notice though is that whenever I told people this they would be shocked and say "Oh I'm sorry!!" and act like it was this terrible thing, up until about maybe 2002/3 at which point it just changed to being a totally normal piece of info, like I'd told them we had a pet cat or something. Of course I was older then - but it did seem by that point that more than half of my friends' parents were no longer together.
When I was 8, so in the mid 90s, a teacher told my mum I was "disturbed" and it was because I was from "a broken home".
(Just neurodivergent, but thanks judgy teacher!) I cannot imagine a teacher saying such a thing to a parent today.
I did split up with DS1's dad before he started school, and I think it was because the stresses of early parenthood really highlighted and excacerbated the cracks which were already there in our relationship, which I had ignored up until then because I thought that they were normal and/or "all men" were like that (my dad,clearly, not being the greatest role model!) or they didn't really affect me so deeply when I was more independent, working etc.
Once I was vulnerable with a child and fully dependent on him I was absolutely miserable because he was an emotionally abusive bastard, and plus it became completely obvious he didn't care about me at all and it was a major turn off that he was not as obsessed with our child as I was.
Totally different with DH (dad of my other kids) but I had the advantage that I already had a child when we got together so I knew what I was looking for. I wouldn't have had a clue before I had a child for real.