Because it is never "the government". It is always a small cabal inside the government. It is always an elite group of bankers and financiers that aren't even part of the government that have successfully fooled the people.
Like I mentioned, saying "the government" committed 9/11 is by default creating the assumption that every member of Congress (Ron Paul included) knew the plan and helped; that every senate aid was helping guide the operation; that the assistant to the Secretary of the Interior was calling friends and telling them not to fly. It just is extremely absurd, much less believable - which is why it is the most common propaganda used against 9/11 truth.
"In the beginning of a change the patriot is a scarce man, and brave, and hated and scorned. When his cause succeeds, the timid join him, for then it costs nothing to be a patriot."--Mark Twain