Losing your planet isn't the end of the world.
Why it is hard sci-fi
Soft. The 2005 BBC adaptation of Douglas Adams. The shows sciences are jokes that hold up. The Infinite Improbability Drive is a parody of every confused FTL theory and is internally consistent in its silliness. The Babel fish is a parody of universal translators and is also a worked piece of biology. The Vogons are a parody of bureaucracy and are honest about how a bureaucracy actually destroys things.
Science inside it
No working physics. The shows interesting model is the Guide itself, a recursive, self-updating reference work that has commercial sponsors, a market position, and a marketing team. That is one of the cleanest portrayals in fiction of what a generally trusted oracle looks like under capitalism, and it is the joke.