Why they exist
FDA labeling rules require individual doses only when the ingredient is disclosed separately. A 'proprietary blend' groups everything into one weight, hiding how much of each ingredient is in there.
The math they don't want you to do
If a '6g performance blend' contains citrulline, beta-alanine, betaine, and taurine — and citrulline needs 6–8 g by itself for effect — then everything in that blend is underdosed. Guaranteed.
The tell
The ingredients listed FIRST are usually the biggest by weight. If a stimulant is listed first, that's where most of the 6 g went. The rest is dust.
The rule
If the label doesn't tell you how much of each ingredient is in one scoop, you don't know what you're taking. Move on.