I think part of it is something else - ease of use and ease of access.
The “world that makes sense” product exists already:
https://www.elementvape.com/box-mod-kits
While I was vaping I mixed my own liquids though, as the cost savings was immense and I could easily lower the nicotine mg/ml on my own until I quit it altogether.
Yeah, they had started limiting what you could buy in Sweden as well. My last time mixing I bought a silly amount of 18mg/ml 10ml strong menthol bottles and large 70/30 PG/VG bottles and ended up with my own 3mg/ml mixture that still tasted menthol, although not as overwhelmingly so.