OK, in Universe there is a weird plot quirk that plays into this subject of Atlas:
By the time Tina was playing Bunkers and Badasses in Borderlands 2 Atlas didn’t exist on Pandora. Athena pretty much ran through them before Jack bought them out. There would be no reason for her to put them in the game, or at least as much reason as there would be to have S & S Munitions back in the game or Scav.
Atlas doesn’t exist until after Tales from the Borderlands, and at that point their only item is a Hyperion shotgun with Atlas branding, the late great “Company Man”. Basically the closest you got to a Butcher in TPS. One thing they didn’t make explicitly clears was where Rhys stood in the hierarchy of Hyperion. Vasquez was dead, Helios was down, and yet, they are a presence in BL3, with no indication of who was running the company, or from where. It wasn’t Rhys or Vaughn, that much we know.
By the time Borderlands 3 is in play Atlas is struggling to avoid being taken over. Their having a small product line and limited inventory makes sense, as does their having niche features since Atlas was so keen on keeping all their patents to themselves (Marcus’s Promethea Echoes explain it). They likely couldn’t afford to be sued by other companies for infringing on theirs.