Measuring added sugar by volume makes little sense. You can add sugar to water and the liquid volume hardly changes. And volume of the sugar depends on crystal size. It works a bit better for alcohol, as that is mixing of two liquids.

Measuring mass makes much more sense and in EU all nutrition labels show sugar per 100g of product (sometimes additionally 'in one serving', but that is quite arbitrary). And that is perfectly enough to compare products. I routinely check labels of picles - many of those have insane amounts of sugar, for no good reasons.

It won't happen because the sugar industry lobbies very actively against this sort of labeling. They specifically don't want you to be able to do those sorts of calculations when buying products, which is why they use a completely arbitrary measurement system for the nutrition label in the first place; most people can't visualize what 60g of sugar even looks like without a scale, but they can definitely visualize ~8% of a can's volume.

while I'm all down for shaming the food industry into maybe not stuffing everything with added sugar, some of us need the amounts too.

As someone with type 1 diabetes, I need to know how much of everything (but especially carbs and kinds) to best guess how much insulin I need to dose before eating. Certainly there is a whole world of deceptive nutrition packaging to break down that doesn't help here, but the specific things you *must* report help to keep the labels honest enough to be workable.

I think the real issue is consumers have no idea what half of the ingredients are, or why they might or might not care about certain aspects of food. Nutritional science in general is very poorly researched. It's hard to get accurate data about what a diet does to people. Aside from locking someone in a room, feeding them everything they are to eat and controlling their activity (which paying volunteers in studies of that intensity is too costly for more than like n=1 studies), everything else is very unreliable. Many studies are backed up by surveys asking participants for what they ate for breakfast 6 months ago. As you might expect, no one remembers this crap, much less in useful detail.

Forgot I posted this, apparently I did not have my account set up to notify me to replies in my threads. Learning curve!

It's exactly like this where I live. Not only sugars, but also fats -specifying which of those are saturated- and many other components. I think it's actually an EU regulation.