So, if it's patently obvious why this is happening, is the issue just that politicians are SUCH pathological liars that they can't tell the truth even if the truth is useful, clear, and provides an obvious cause-and-effect?

Ask a politician if it is currently raining while they're soaked to the bone from it, and they'll say "weather patterns aren't universal, we're not prepared to answer in either direction on that question, we'll circle back in a couple days."