light industry isn't meant to turn a profit, it's to support your faction's population needs internally.
if that were how it actually works, sure. but it isn't. as long as you have decent accessibility, afaik it makes no difference whether you produce goods locally/in-faction, or import them from out-of-faction. out-of-faction imports don't cost anything.
but regardless, even if it it would work that way, this logic could be applied to pretty much any industry. food for your own population, ore for your own refineries, metals for your own heavy industries, armaments for your own ground defenses, fuel for your own spaceports, supplies for many of your different industries, etc. unless you own Volturn, literally every good that an industry on one of your colonies can produce will be in demand by another industry you can build on the same colony, or on other colonies of your faction.
but that doesn't change the fact that LI does export its produced goods just like any other industry. i don't mind if not all industries are meant to be profitable (and i actually think HI shouldn't be, as mentioned). but saying that if LI isn't profitable, it is clearly because it isn't meant to be, seems a bit silly -- especially considering the use you describe doesn't actually exist in terms of gameplay (unless you have really bad accessibility for some reason, so that you run into shortages when importing from out-of-faction).