Today I had a can of soup. The can had a pull ring on it so I didn’t have to use a can opener.
Why don’t more canned foods utilize pull rings? Is it because of cost? It seems to me that would be minuscule.
From https://money.howstuffworks.com/food-cans-pull-tabs.htm :
Tom Crothers has worked at DRT [a pull-tab lid manufacturer with patents] for 40 years, most recently as its VP of sales. We asked him why — nearly 60 years after the invention of the easy open can — only some canned foods come with pull tabs while most still require a can opener.
“I wish all cans had easy open tabs — we’d be even busier,” jokes Crothers. “Basically, what it gets down to is a cost issue. Easy open ends are more expensive than ‘sanitary ends’ [the sealed lids that require a can opener].”
The article has a few more details to back that up. It’s a short read so I didn’t want to quote too much more for fair use reasons.
It has to be more expensive than traditional cans. But as a matter of anecdotal fact I experienced just yesterday in attempting to open one of those cans, the pull ring pulled right off and flew into the air. I opened the can with a regular can opener and then had to go find the errant ring far away on the floor.
The micro-grooves are a possible though unlikely source of contamination. The only point of those things is if you don’t have convenient access to a can opener, such as when camping. Which isn’t much good when the damn thing doesn’t even open with the pull tab!
One pattern I’ve noticed is that heat-and-serve or ready-to-eat foods are more likely to come with the pull tab, while foods that will be used as ingredients in some other recipe usually don’t. Probably the people buying the latter category are more likely to have a well-stocked kitchen, and to be opening their cans there.
You don’t know your own strength, Bullwinkle. 
What I don’t like about them is the splatter they can cause when the lid snaps open.
But when camping, and we don’t camp much, there’s always some goddamn thing you need and don’t have. And not having a can opener when you need one is a catastrophe. .
IMO that’s the point. If it’s something people would (foolishly) want to eat while driving, it’s a pull tab. If not, not.
The trivial added expense works for a convenience food, which is already priced for high margin, but not so much for commodities like canned vegetables.
Are people really eating Chef Boyardee or sardines while driving? Both are opened with a pull tab. I had mini ravioli for lunch yesterday.
When I was a kid in the 60’s sardines had to be opened with a little key that was stuck on the bottom of the can. I know pull tabs were already invented then. What was the deal with that key?
This Can opener → Twist Key - Wikipedia says they were invented in 1866 and were the very first version of a self-openable can.
As a little kid shopping w Mom in the early 1960s I recall lots of canned foods packaged that way. And some non-food stuff although I’m struggling to remember what they might have been.
ANd yes, between early 60s and late 70s those keys almost disappeared. Almost. That anything is still packed that way now versus the modern pull tab + peel-away insert top is almost certainly a matter of inertia. This factory has that gear to use these cans …
“Oh, no, my pudding is trapped forever!”
I don’t know about driving, but it is common for people to do things like bringing in one of those cans to work for lunch: Open it up, pour into a bowl, and pop it in the microwave. The work breakroom might have a can opener, but lots of luck finding it.
They’re also popular at food giveaways for the needy. Homeless people might not even have access to a kitchen or can opener.
You’re going to be eating SPAM a lot during the zombie apocalypse; get used to it.
Since it appears the FQ was answered …
On your keychain, in your glove compartment, in your basic camping kitchen kit.
They’re cheap. They work. QED 
“Take my pen knife, my good man!”
I found a can of Hereford Deli Beef in our pantry that opened with a pull ring. Don’t know how it got there but thought it was going to be gross.
It was exquisite. Had several slices on saltines. SPAM could never compete.
I ask you: what’s the point in surviving a zombie apocalypse if the SPAM kills you in a couple years?
In my local (UK) supermarkets pretty much all but the cheapest budget range cans are now pull ring, regardless of the contents.
I actually noticed it when we had supply chain disruption and the cans requiring a can opener were the only ones left on the shelves- which seemed odd, you’d expect people would snap up the cheap stuff ‘just in case’. It left me wondering if some people here don’t have a can opener any more, the only use mine ever normally gets is when a pull ring doesn’t work.
ISWYDT.
Cans of tennis balls used to have a key attached to the bottom that you had to break off and use to open the top of the can – much like sardines.
Like Filbert’s experience, here in Australia the vast majority of canned goods have the ring pull mechanism.
Except beetroot for some unfathomable reason.
As someone who had done the costing on hundreds of “private label” (store brand) products for several retailers, it’s mostly down to cost.
Customers of more convenience oriented canned foods might be willing to pay an extra nickel for a pull top, but buyers of basic canned foodstuffs often aren’t. So chicken noodle soup usually is in a pull top can, but kidney beans are not. Sometimes a store brand will try to cut a nickel out of the cost by using a non pull top can for soup (for example) but customers are likely to further downgrade the quality perception versus the brand name.
A lot of “cost innovation” (enshittifcation) happens first in the private label space. If it succeeds, it spreads to brand names.