There is potentially a lot of technical problems with the idea. It would really depend on how the game currently handles loot pulled from Collections and how traits are/would be generated on them. Like if you were to pull Dust Rock Blues from Collections, are the trait possibilities still programmed into the game at this point? And does it even know what it should do when pulling from Collections in the first place? The only reason I think there could be problems is really because there are a small amount of weapons in the game that have traits that can generate on them depending on their sources that they are obtained from. And I'm talking about the Origin Trait, Accelerated Assault, specifically and the weapons it can roll on. Or another thing. What if you pull the non-Brave Arsenal version of Hung Jury or some other weapon that's been updated a million times. Weapons updated like that don't show that many versions of it in Collections, so you'd usually be limited to the up-to-date versions of them, locking you out of certain traits or, potentially, elements from them regardless. And then another thing. I'm pretty sure certain older weapons currently don't show up in Collections if they've never been earned at all on your account. I'm not really sure what the best solution to that would be as it wouldn't even be "re"-acquiring them at that point. I guess that's just missed loot forever in that case. If the devs were to make something like this happen, I'm sure some or even a lot of the things I stated could be ignored, but there would be a lot to think about, and I really don't think they have the time to make it happen at this point. I miss my old weapons too, but that might just be how it remains.

Basically you saying is give me loot with playing game

Yup. Needs to happen. Even if it costs a substantial amount of currency.