It's not a mystery at all afaics. They do spoil over time if not used, and you don't need that many of them because of their intense flavour so it makes sense to only have a small jar open at any given time so they don't spoil.
As for getting them out of a jar I really don't know what to say. It's a small jar so use a small spoon? That's what I do, and I presumed everyone else also did.
Your life must be pretty good if getting capers out of a jar is something you have time to trouble yourself thinking of optimising.
Here's something which could be a genuine market mystery (which I know the reason for but it's kind of a fun one to ponder if you don't): Why is the label on angostura bitters always too big for the bottle?
Last time I bought capers, even my standard-issue Ikea teaspoons were too wide to fit in the jar.
Now, my fancy tiny espresso-stirring spoons that are small enough, but on the other hand; those are _too small_ to actually eat anything with them conveniently.
The mystery is why the glass is long and thin, not why it is small, if I understood it correctly. You could have a glass with the same volume where you can use a normal spoon.
Pretty sure that is most simply explained by prominence on a supermarket shelf. Something short and stubby is hard to see so people don't buy it, which is true in general, not just for capers. That's why you only really see that form factor on things like free sample jars and one shot jam jars that go into airplane meals, hotel buffet breakfasts etc- things where the manufacturer isn't fighting for prominence with other brands.
That theory is also supported by the fact that big caper jars typically have the same aspect ratio as jars of other things (ie they aren't just a scaled up version of a small caper jar). At that size they have enough prominence on the shelf.
This feels like one of those things where you're saying something that is maybe technically correct, so you can feel smart, but has no bearing on reality.
A store near me sells capers in a short-and-fat glass jar (which even a large spoon can fit in easily).
I've been able to leave those in the fridge just fine for 6 months with no noticeable change in quality... just like the tall-and-narrow glass jars.
Based on my personal experience of these two jar shapes, any difference in spoilage-rate is imperceptible.
I doubt the surface area matters. The volume of air and therefore oxygen you introduce every time you open the jar is the important factor. I would have thought that oxygen will dissolve in the liquid over a day or so even with a small surface area between the air and the liquid.
This amuses me because I tend to use a fork even though I have spoons that can fit in my jars specifically to strain off the brine. I usually use capers to make salmon and cream cheese bagels, and I don't like drippy bagels.
One manufacturer at least has it figured out. These are what I’ve been getting in the US for a while now from places like Sprouts (Fresh Thyme), and Whole Foods. Even using a fork like others mention, it’s still just easier with this jar.
I suspect that's for regular olive-sized capers with the stem attached? The article is about peppercorn-sized baby capers, where you could fit thousands into a jar that big.
No. These capers are the size of black peppercorns, though I never count them, it’s a very large number of them, though they have not been in stock since the end of the quarantines during pandemic.
Capers are very common in my family's refrigerators, but still mostly used for a single dish (Königsberger Klopse). And the jars have been tiny for as long as I can remember. So it seems to be a universal design decision.
As for getting them out of a jar I really don't know what to say. It's a small jar so use a small spoon? That's what I do, and I presumed everyone else also did.
Your life must be pretty good if getting capers out of a jar is something you have time to trouble yourself thinking of optimising.
Here's something which could be a genuine market mystery (which I know the reason for but it's kind of a fun one to ponder if you don't): Why is the label on angostura bitters always too big for the bottle?