Litter. And pull tab litter ending up slicing peoples' feet open. And idiots opening their beveragem dropping the pull tab inside, drinking it and slicing up their throat. No, they don't go all the way down, but they'll play hell with the soft tissue in the back of your mouth.
"Nurishment" cans, often found in the foreign foods aisle, still use the old style ring pull.
I'd guess it's because they are intended to be drunk like a soda can, but packaged in a tinned-sweetcorn style can. Those cans are unpressurized, use steel, and have significantly thicker walls (= more material cost)
I do wonder why they never decided to switch over? Perhaps they consider it part of the brand? Perhaps they still run the same canning factory for decades and without expanding sales don't see a need to retool? Perhaps the 2 pence per 1.50 product are insignificant when they have quite a market niche.
I remember grownups telling me how terrible the change was, because any dust on the tab now flipped downward and fell into the can, whereas before it was pulled away.
as a kid, we'd break the tab from the pull ring and then insert the fat end of the tab into the slot on the pull ring. we'd pull the ring back on the pull tab and release the ring flying. if we were really bored, we might actually go find the ring and do it again. i was surprised at how far these could fly like this.