I don't care what they are called now. They weren't called that in the UK in the 80s.
Levis had that extra room. That extra room. That was their schtick!
We had boot cuts, flares, jeans with ready made rolled up cuffs, nothing came between Brooke and her Calvin Klein's or Claudia and here whatever they were's. And we had baggier, looser jeans - think early Madonna, Dexy's even! But they weren't called Mom jeans at that time.
Those looser, high waisted, straight legged (not boot cut, baggies or flares) have always existed, since jeans have existed I would imagine, But the name? That's way more recent.
That's all I am saying. I am alive, was alive in my teens into 20s in the 80s. And we really didn't call them that! We just called them jeans and it was usually the brand, the label that defined them if anything did.