Your understanding is wrong. Cheap vape liquid from dodgy sources years ago used diacetyl. This was quickly discovered and vapers stopped purchasing it and it immediately became prominently listed on pretty much all products what proportion of vegetable glycerin and/or propylene glycol is being used and that those are the only ingredients aside from nicotine and flavoring. If anyone is still using diacetyl they are probably dodgy gas station disposables from China.
"Diketones such as diacetyl, acetoin and acetyl propionyl are present in a number of these flavourings as they add an authentic buttery and creamy taste to the e-liquids produced by many manufacturers."
They said "some". Your comment refers to the possibility that some may still, as in the gas station. That fits the criteria for "some".
The idea that conscious consumers reading ingredient labels will solve 100% of such a problem is also kind of silly. Look at the obesity problem as an example of how well labeling works - it's possible to read the labels and be careful about your food intake, but most do not.
