Well, some labeling is mandated by the FDA.

I can see proprietary listing as "secret" ...but CAFFEINE which is
problematic for many people.... they should list that.
It is the MAIN ingredient after all. What is most troubling is
that the DECAF has caffeine content labeled on it...a tiny 6mg,
but the stronger products...it is secret. Now come ON!

The soy labeling you mention is part of the allergy revealing
FDA labeling. When that went into effect, then, with the statements,
"contains soy, or gluten, or nuts" and "manufactured on equipment that makes wheat products" etc. Also choline is derived from soy lecithin. And this product contains choline

Most of the "soy" ingredients are soybean oil or natural soy lecithin which is a suspending agent.. Inert ingredients, as you point out... are NOT active agents like CAFFEINE.
From your example:
These items are excipients added the to the product, to improve flow and management of the powder, going into the machines, and as such are not part of the "active ingredients".
Also some B-complex derives from Brewer's yeast, and hence quantifying them is not easy or possible. I suspect the FDA just permits "brewer's yeast" to be used on the labels, that contain it.

Some of the better products have detailed listings on them.
Your example is quite a LONG list of ingredients compared to most.

If you buy a taurine product....like I do with my cats, or for diabetic use, or whatever...it will say how much taurine is in each capsule. But in 5 hr energy, taurine is not quantified. Hence the "impression" is that not much is in there.

So my major problem with this product, other than the huge price for something that contains pennies worth of ingredients, is that the CAFFEINE is not quantified. Also the B6 is quite high, and for some people who get "hooked" on 5 hr energy, because of the kick it provides and the caffeine withdrawal that can occur when not used, the B6 can become problematic for some people.
I think 10mg of B6 would have been plenty.