Because it's a conspiracy theory. Conspiracy theorists often need to construct some sort of bad actor to help them fabricate the missing pieces of the puzzle in their theories.
...You do know...
The ENTIRE rest of the world calls TIGHAR and anyone else who investigates AE "Conspiracy Theorists..." In fact TIGHAR is the largest most populated and known conspiracy theory group I can think of. Am I so nutty the Conspiracy Theory Club rejects me and calls me a Conspiracy Theorist. LMAO.
So seriously does nobody find all the discrepancies with Amalgamated Wireless suspicious?
The logs from the Navy ships looking for her show "Distinct Japanese music playing" on her frequency at several of the times of her scheduled transmissions. How could there not be some sort of conspiratorial foul play going on? I tend to think it was someone who wanted to point the finger at the Japanese rather than the Japanese themselves jamming the frequency.
That does not mean they are right. To have a conspiracy theory, one needs a conspiracy.
Neither Crashed and Sank (C&S) nor Niku are conspiracy theories in any sense.
C&S: After failing to find Howland, she ran out of gas (we're low on gas....her words), she crashed, splashed or landed on the ocean and was not rescued. No debris was ever found, and she never broadcasted "we're gonna be in the Hudson", "Mayday, Mayday", "oh sh*t", or anything like that. While there is no evidence of this happening, disappearing in the vast Pacific is not that unusual, and is a totally plausible explanation.
Niku: After failing to find Howland, and low on gas (her words), she found an island that is roughly on the line that she was flying (157/337....her words), landed (post loss signals, Bevington object, patch artifact, plexiglas, possibly other random airplane parts), attempted to survive (castaway campsite with cosmetics typically used by a 1930's western woman, clam shells, bird bones) and died (bones found). The only possible conspiracy I can find is among the coconut crabs.
Japanese Capture, Irene Bolam, and whatever Lovecraftian thing you have dreamed up
ARE conspiracy theories. They all involve corporations, wealthy individuals, and/or governments conspiring to spy on each other, capture spies, sabotage the flight, or cover up malfeasance. Japanese Capture alone has a number of different endings for Amelia and Fred, with as many different locations and eyewitnesses to the deed.