Where is that coming from? Since when should smuggling only be smuggling if done via missions?
The fundamental issue with non-mission smuggling come from the fact that illegal status for a commodity doesn't artificially drive prices higher as it does in RL, and that there is virtually no risk involved (sadly lack of risk applies to more than just smuggling) , making it not only almost as boring as space trucking, but also less profitable than regular trading.
There are some edge cases where you can make good money doing it, but these are usually side effects of badly thought mechanics or just plain bugs, such as the one discussed in the OP.
And no amount of missions or PP mechanics will fix the underlying problem of the background simulation not dealing correctly with the legal status of goods. And the worrying thing is, FD seem to have trouble really understanding that judging by the fact that for a long time they didn't even make the difference between stolen and illegal goods, and that at last they merely removed the 50% malus on illegal goods, where illegal goods should obviously be on super-high demand (although in small quantities) and therefore sell much, much higher than the gal average (and don't get me started on artificial price ceilings).
I shouldn't have to rely on the special mechanics of specific PP factions to actually make money by smuggling. The inhabited bubble is bigger than that, and I'm pretty sure wherever there are laws, there is a lot of money to be made breaking them if you are skilled enough. Sadly this is only true in a few places atm, and skill doesn't even come into play.
