The ammo you get from the insurgencies is harder to obtain and way more dangerous to transport compared to Empire faction ammo. The price being so high is simply because its rare at least for now, but where it gets odd is that the ammo (such as arch angels) is objectively worse than Empire faction. Please see images below. One might imagine that is something was rarer and harder/riskier to transport that it would also be at least on par in some way with the easier to get/acquire faction equivalent.
This means the only real valuable thing that will ever come from the LP store is the datacores. The modules are the same as empire faction modules but still are harder/riskier to get to market. It seems to me that the pirate LP store is meant to be worth way less than equivalent LP stores in the long run because half of the biggest sellers in the LP stores is ammo and datacores of which only one is really valuable.
I do not know what solutions there could be but it definitely seems that pirate ammo could use a rework. Maybe the ammo stays less damage but has slightly better tracking and optimal ranges. It does less damage but applies better in a brawl or slightly outranges in a kite.