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.
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.
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.
What are you basing your "spoil faster" on?