These weapons are no longer available in the main campaign, notably any of the unique variants or the BFG, due to seemingly being moved to an in-game store pack that isn't automatically set as owned for users of the Fallen Ghosts DLC. Be careful if you buy the DLC on Steam expecting these weapons to appear. You will get the PSG and MDR in the main game, as well as the crossbow, but nothing else. There may or may not be a fix in the works.
Wow - necro-bumping a topic that's been dead for 3 years.
I know you're just trying to help - but you might want to take care and check the dates on the last post - odds are most of the people who took part in the topic aren't even here on the Forums any more - and most of the ones who are will likely be in the other sections.
You are not wrong but then, are you sure that this is only happening if you purchase the game from steam and not directly from Ubisoft Connect store? I purchased the game and perhaps a year later I purchased the FG DLC and I remember I already had a few of those weapons from all the crates I had acquired and since I normally use only a handful of weapons I couldn't tell you if what you are saying is true now or if it was always like that... from the beginning I mean.