You could say the same thing about most products.
Imagine if every food on the market had to pay a million dollars to get certified.
If the FDA wanted to run a generic study on whether vaping was safe, I would applaud it. Even if it charged ten million dollars across the entire industry to fund that study, that would be fine. But making every manufacturer go through an independent highly-expensive process is a product of regulatory capture, not to keep anyone safe.
Even if the individual drugs have their own certification, mixing them and packaging them together requires a new certification. Now of course, the new cert will rely heavily on the existing docs, so it's not like everything has to be re-proved again, but the interaction & effects thereof are scrutinized a bit more heavily.
Of course this is assuming that the goal of the FDA is to genuinely protect consumers.
I'm aware of at least one component - styrene - which has been linked to cancer and is commonly present in fragrances.