well yea, I guess your right, but fighting was never they're main focus, and they obviously never cared about getting better stuff, since they don't have better stuff o.o
You do see a quick scene with Mimiru in one episode, saying she must get stronger. This seems to imply a great deal more time spent leveling up, considering how stubborn she is.
"A friend... or perhaps, a foe. A meddler with a warning." -Helba, .hack//Infection
There's also the episode at the beginning of Sign, when Tsukasa is fighting a Crimson Knight. And then there's the fight where the dothackers were taking down a guardian and Crim fighting Sora.
In those fights, they were fighting because they had to, not because they were concerned with getting stronger. As for Mimiru, maybe she wanted to level up, but she didn't seem too concerned with weapons and such, or maybe she can't find a better one. In one of the episodes, she goes to the dungeon she met Tsukasa in, and opens the treasure chest. "Aww......how cheap..."-Mimiru (refering to the item)
My guess would be that the Sign, being more concerned of matters of a mental nature, simply thought that weaponry appearances were irrelevent in the face of intellectually fascinating storylines.
Either that, or CC corp were really, really, lazy. Take your pick.