What’s with Banshee being a “quartermaster/gun vendor” but he really just gives out mods, mats and bounties?

It's the first time making a post here and I'm feel like I'm still pretty new to Destiny in general, so this probably was touched on somewhere but…. What the heck is with Banshee?

He's what the game calls a vendor, a quartermaster of the tower. He repairs and fixes guns and tools them up for Guardians. But why does he not sell guns? Why doesn't he sell anything aside from mods and upgrade modules and bounties? There are so many vendors that give bounties and missions and stuff, but Bungies couldn't give any of them an actual shop? This is, one of the reasons why I think, prevents Destiny from feeling like an actual MMO in some areas. Because nobody really sells anything, aside from exchanging a billion different kinds of mats and currencies for stuff. The only thing that sort of counts now is the Monument which gives out exotic stuff, but why doesn't Banshee do something like that?

I feel like if he had a rotating inventory of legendary weapons, maybe a small set or even one of each type of weapon, or one weapon from kinetic, power, etc, it would be help a lot. Considering the fact that we mostly get weapons from RNG drops and stuff, I feel like it would help with the RNG fatigue a bit when you know there's at least a legendary weapon you can use from Banshee. Random rolls, of course. Doesn't the old man want to make any money? It can even cost legendary shards, glimmer, the actual currency that the setting uses.

And why stop there? Maybe Banshee could provide services to Guardians for their weapons. Maybe he could retool weapons to have something re-rolled, or you could pay him a lot of mats and currency to give you the perk you want? Anybody else pick up what I'm putting down? Yeah, there are some NPCs that give out some gear, like Zavala and the armor, and Hawthorne gives you some poopy stuff for beginners, but nobody wants that stuff and isn't it the job of the quartermaster to, you know, give out weapons?

EDIT: I am aware of the gunsmith materials and he makes you guns, but why can't he just sell stuff in addition to that?