Now that is something that has also bugged me: they are always being in fights with Jaffa, near gates, or other places, where they beat the Jaffa hands down - but never take any of their goodies. More precisely of course we never SEE them do it.
In "Forver In a Day" for example, they COULD have done it, given what technology they have come through with them.
What it may be is the standing rule that you can't assume the dropped weapon is safe and not booby-trapped: just look at "Platoon" for examples of not thinking about traps. Even better is "Surviving the Game", which shows the same with weapons.
BUT, in general - they could whip them all back through the gate for specialist assessment, renovation and re-use.
[PS. When did Tea'lc get his helpmet back - he dropped half his armour in COTG, but gets it back by Bloodlines? (Same principle? Are they collecting? Doh! Could be from the dead Jaffa in COTG...]