Because they are just behind nearly everything. On an individual level, all of those things make sense, but when taken as a whole, it amounts to a massive list of things that the Legion are behind. No one force is behind that many different problems in one region. Its a level of systemic manipulation that only exists in conspiracy theories. Its like, in Fallout 4, wastelanders try to push this idea that The Institute is behind this ultra mega conspiracy, and that they are actively behind every ill in The Commonwealth, but when you actually get to The Institute you find out that -The fall of the CPG was the fault of the wastelanders, not The Institute. -The Broken Mask Incident was just an accident, and The Institute wasn't trying to infiltrate people with synths. -The destruction of University Point was just Kellogg going on a rampage. -Most synths found in the general populace are not part of an Institute plot, they are actually synths the Railroad hid in the general populace. There is a moment where they pull the curtain back, and reveal The Institute to not be this comic book evil, mustache twirling, villains who are just behind EVERYTHING, and that the things attributed to them are actually part of a large and more complex series of events. The Legion has no moment like this, they are just behind almost everything, have manipulated almost everyone, and are the mustache twirling villains behind most all the problems of the Mojave. This is a baseless argument as Tim Cain, Chris A, and Josh Sawyer, have all talked about a number of things they DIDN'T like with Fallout 3/4. This argument is nothing but mental gymnastics to try to make up excuses as to how the developers held so highly for making Fallout 1/2 could like something you don't.