I don't know much about inscriptions, but let me see if I get this right.
In a game where everyone wants the absolutely best items, inscriptions are just another way to buff an item. So not only are you looking for a weapon that has the best dmg (or whatever), but your looking for a weapon that also has the best mods, best construction parts (hammer grips, bow strings, etc), and an inscription slot so you can add the best inscription to it. This way, there could not be a better weapon for that class/use.
Because your weapon doesn't have an inscription slot, it means that it can never be as good as the best weapons, and since the value for weapons below "the best" are very low since nobody wants them, your normally expensive item is now worth not as much.
Hopefully I got that right.
Bummer
I'm sure you could make some PVE noob player's day though if you gave them a good deal on it.