I think there are two related problems -

one is contamination of black market carts

the other is the rise of teenage nicotine intake

My understanding is many of the federal laws are meant to address the latter, while the local laws like the MA vape ban meant to address the former are now being rolled back.

Last I checked they banned all cartridges with flavor at the federal level, but made an exception for the liquid you put into your homebuilt equipment.

I am not sure what this accomplishes. Perhaps making it difficult enough that teenagers don't vape?

Here is the source of the regulations: https://www.fda.gov/regulatory-information/search-fda-guidan...

(I used to vape, so I'm familiar with the landscape, but am no longer personally invested.)