I don't think it is a deliberate treatise on capitalism (talking specifically of the first 3 'Fallout' games, while 'Borderlands' is a bit more on the nose), but it lends itself to being one because in exploring how the world was controlled then destroyed, out-of-control capitalism provided an easy, observable vehicle by which to tell their story. So it can easily be taken as one if that is where you want to go.
The villains, for obvious fictional reasons, went far beyond the average apathetic, greed-driven, and incompetent billionaire that we see today and instead were portrayed as insidious, devious, conniving, sociopathic, and dastardly people who were willing to murder billions of people for their chance to cement absolute control in the new lawless society that came after. There's no parallels beyond the basic tenets of capitalism to actual reality so don't get your panties twisted. As with the movie "Don't Look Up" or other games like "The Outer Worlds", it is a surrealist and satirical take on the subject and can't actually happen.
"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far."
"Universal compassion is the only guarantee of morality."